TST: Fixturize series/test_dtypes.py
This is in reference to issue #22550
Hello @Anjali2019! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/series/test_dtypes.py`](https://github.com/Anjali2019/pandas/blob/a57cef8487a7d55d9b5ecf49fd30f8df3c209c50/pandas/tests/series/test_dtypes.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22967?src=pr&el=h1) Report
> Merging [#22967](https://codecov.io/gh/pandas-dev/pandas/pull/22967?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/03181f0569c8b1f93f620a2986b4f174f9b6179b?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/22967/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22967?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22967      +/-   ##
==========================================
+ Coverage   92.19%    92.2%   +<.01%     
==========================================
  Files         169      169              
  Lines       50812    50812              
==========================================
+ Hits        46847    46849       +2     
+ Misses       3965     3963       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <ø> (ø)` | :arrow_up: |
| #single | `42.37% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22967?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/22967/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `98.11% <0%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/22967/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `86.23% <0%> (+0.2%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22967?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/22967?src=pr&el=footer). Last update [03181f0...a57cef8](https://codecov.io/gh/pandas-dev/pandas/pull/22967?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @Anjali2019  @Anjali2019 these don't necessarily have to be 1 PR per file as these are straightforward search/replace.