Ignore underscore references in type annotations (#9036)
## Summary
Occasionally, valid code needs to use `argparse._SubParsersAction` in a
type annotation. This isn't great, but it's indicative of the fact that
public interfaces can return private types. If you accessed that private
type via a private interface, then we should be flagging the call site,
rather than the annotation.
Closes https://github.com/astral-sh/ruff/issues/9013.
