DOC fix EX02 algorithms.factorize docstring
- [x] Part of #51236
- [ ] [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
- [x] 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.

Towards #51236.

Fix EX02 docstring errors for :

`pandas.factorize`
`pandas.Index.factorize`
`pandas.Series.factorize`

thanks! can you remove them from the excludes list? Done. Thanks for the review @MarcoGorelli  The Docstring validation should be good now.