Fix showing "None" as ylabel in :meth:`Series.plot` when not setting ylabel
- [ ] closes #46129
- [ ] [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).
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

[here](https://github.com/pandas-dev/pandas/issues/46129#issuecomment-1055224345), Mctoel mentioned that if series.plot(kind=pie) does not specify `ylabel`, "None" will appear as ylabel in the figure.
![image](https://user-images.githubusercontent.com/42494185/159170646-8e4013f3-9be5-4873-92f7-7b948666efbc.png)

thanks @iansheng 