CI: add validate_unwanted_patterns to known_third_parties

[MarcoGorelli]

• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff

By using seed-isort-config, the known_third_party setting is automatically populated and alphabetically sorted. This is a cleaner solution which doesn't require manually adding third parties to setup.cfg.

Furthermore, it catches an existing inconsistency: currently, validate_docstrings is set as a known third party, while validate_unwanted_patterns isn't. Neither should be, IMO.

[TomAugspurger]

We had this and removed it in #28272 (see some discussions there). I think I struggled the most with it, dunno if it hit other contributors.

[MarcoGorelli]

@TomAugspurger thanks for pointing me towards that - OK, am happy to not add seed-isort-config if it causes issues.

Should validate_docstrings be removed from the list of known_third_parties though?

[TomAugspurger]

Don't know. It's not in the pandas namespace, so probably not? Don't have a strong preference though.

[MarcoGorelli]

Sure - have removed seed-isort-config and added validate_unwanted_patterns to the list of known 3rd parties (I presume they should either both be there, or neither?)

[WillAyd]

I think this is fine

[jreback]

lgtm

[TomAugspurger]

Thanks!