DOC: Fix EX03 flake8 errors in docstrings
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

For `pandas.Series.cat.set_categories`
<img width="459" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/bbde9ea6-5d8f-4597-a8ab-3d873af66863">

For `pandas.Series.plot.bar`
<img width="308" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/d59ffaad-ae12-4ca1-b1ee-cb2da4126a26">

For `pandas.Series.plot.hist`
<img width="379" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/a36e946c-1774-4b7b-a175-e2beb7934385">

Some errors remain, but unrelated to EX03.

Could you resolve the merge conflict? Thanks @luke396 