Update return type of argparse.ArgumentParser._parse_optional

[yangdanny97]

Seems like starting in 3.12 this function returns an optional list of 4-tuples, instead of a single optional 3-tuple

https://github.com/python/cpython/blob/3.12/Lib/argparse.py#L2320

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

scrapy (https://github.com/scrapy/scrapy)
+ scrapy/cmdline.py:29: error: Return type "tuple[Action | None, str, str | None] | None" of "_parse_optional" incompatible with return type "list[tuple[Action | None, str, str | None, str | None]] | None" in supertype "argparse.ArgumentParser"  [override]
+ scrapy/cmdline.py:37: error: Incompatible return value type (got "list[tuple[Action | None, str, str | None, str | None]] | None", expected "tuple[Action | None, str, str | None] | None")  [return-value]