TST: tests for inconsistent indexing with datetimes

- [X] closes #9336
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20550?src=pr&el=h1) Report
> Merging [#20550](https://codecov.io/gh/pandas-dev/pandas/pull/20550?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bc37ea2e05019a89adaa48159b220483598d1898?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/20550/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20550?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20550      +/-   ##
==========================================
+ Coverage   91.84%   91.84%   +<.01%     
==========================================
  Files         153      153              
  Lines       49499    49505       +6     
==========================================
+ Hits        45460    45466       +6     
  Misses       4039     4039
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (ø)` | :arrow_up: |
| #single | `41.88% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20550?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `94.99% <0%> (-0.09%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.22% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/accessor.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWNjZXNzb3IucHk=) | `98.71% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `93.14% <0%> (ø)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.12% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.68% <0%> (+0.04%)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/20550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `92.09% <0%> (+0.08%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20550?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/20550?src=pr&el=footer). Last update [bc37ea2...f7fb642](https://codecov.io/gh/pandas-dev/pandas/pull/20550?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 also add as a comment the original issue number Done, happy to contribute! Please, let me know if I must make any additional changes. Done! :-) thanks @jcontesti 