TST: Local conftest for test_offsets.py
- [x] closes xxxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Continued from #17622 per comments. Looks like `offset_types` property can be replaced entirely with a fixture.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=h1) Report
> Merging [#17825](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9f0ee53dad3bd14a3f0475a29d326c89c6b6aced?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17825/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17825      +/-   ##
==========================================
- Coverage   91.26%   91.22%   -0.05%     
==========================================
  Files         163      163              
  Lines       49980    49980              
==========================================
- Hits        45613    45592      -21     
- Misses       4367     4388      +21
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.02% <100%> (-0.03%)` | :arrow_down: |
| #single | `40.24% <100%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tests/tseries/conftest.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL3RzZXJpZXMvY29uZnRlc3QucHk=) | `96.77% <100%> (ø)` | |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.38% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.74% <0%> (-0.1%)` | :arrow_down: |
| [pandas/tests/indexes/conftest.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL2luZGV4ZXMvY29uZnRlc3QucHk=) | | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17825?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/17825?src=pr&el=footer). Last update [9f0ee53...69db510](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=h1) Report
> Merging [#17825](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9f0ee53dad3bd14a3f0475a29d326c89c6b6aced?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17825/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17825      +/-   ##
==========================================
- Coverage   91.26%   91.22%   -0.05%     
==========================================
  Files         163      163              
  Lines       49980    49980              
==========================================
- Hits        45613    45592      -21     
- Misses       4367     4388      +21
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.02% <100%> (-0.03%)` | :arrow_down: |
| #single | `40.24% <100%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tests/tseries/conftest.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL3RzZXJpZXMvY29uZnRlc3QucHk=) | `96.77% <100%> (ø)` | |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.38% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.74% <0%> (-0.1%)` | :arrow_down: |
| [pandas/tests/indexes/conftest.py](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=tree#diff-cGFuZGFzL3Rlc3RzL2luZGV4ZXMvY29uZnRlc3QucHk=) | | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17825?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/17825?src=pr&el=footer). Last update [9f0ee53...69db510](https://codecov.io/gh/pandas-dev/pandas/pull/17825?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!

keem em coming!