Fix import format pandas/tests/indexing
- [x] xref #23334
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Ran `isort --recursive pandas` and then checked imports using `isort --recursive --check-only pandas`

PR capped at 20 files, but 21 files changed because it includes setup.cfg which has also been changed.

Hello @amphy! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/indexing/common.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/common.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/conftest.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/conftest.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/interval/test_interval.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/interval/test_interval.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/interval/test_interval_new.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/interval/test_interval_new.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_callable.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_callable.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_categorical.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_categorical.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_chaining_and_caching.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_chaining_and_caching.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_coercion.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_coercion.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_datetime.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_datetime.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_floats.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_floats.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_iloc.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_iloc.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_indexing.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_indexing.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_indexing_slow.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_indexing_slow.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_ix.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_ix.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_loc.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_loc.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_multiindex.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_multiindex.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_panel.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_panel.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_partial.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_partial.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_scalar.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_scalar.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_timedelta.py`](https://github.com/amphy/pandas/blob/e141a562b58d2a1ae31dca338a609764e984e108/pandas/tests/indexing/test_timedelta.py) !

 lgtm. ping on green. @amphy Do you have to rerun `isort`? I still have issue travis-ci. And I also saw you had before.  @thoo Yeah, I re-ran isort after checking the pandas/tests/indexing directory again with isort and it seems to pass what was giving me trouble earlier with Travis CI (My issue was that I was getting an error from ./ci/code_checks.sh so I ran that locally which revealed that I was getting some errors from isort) @amphy  I looked at your log before and we are getting the same error. I have 3-4 commits with similar errors.  I  think it might be related to rebasing with upstream/master.  Thanks for the reply. Hopefully it will solve.  @amphy  Thanks. Mine is fixed too. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=h1) Report
> Merging [#23351](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/437f31cb609372f465aaa853bf4b2299a9550716?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23351/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23351      +/-   ##
==========================================
+ Coverage   92.22%   92.22%   +<.01%     
==========================================
  Files         169      169              
  Lines       51258    51261       +3     
==========================================
+ Hits        47274    47277       +3     
  Misses       3984     3984
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.66% <ø> (ø)` | :arrow_up: |
| #single | `42.23% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/23351/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.91% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/arrays/sparse.py](https://codecov.io/gh/pandas-dev/pandas/pull/23351/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3NwYXJzZS5weQ==) | `91.84% <0%> (ø)` | :arrow_up: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/23351/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `97.46% <0%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/23351/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `89.28% <0%> (+0.05%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=footer). Last update [437f31c...8f654d5](https://codecov.io/gh/pandas-dev/pandas/pull/23351?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback All green now