[`pyupgrade`] Avoid PEP-604 unions with `typing.NamedTuple` (`UP007`, `UP045`) (#18682)
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## Summary
Make `UP045` ignore `Optional[NamedTuple]` as `NamedTuple` is a function
(not a proper type). Rewriting it to `NamedTuple | None` breaks at
runtime. While type checkers currently accept `NamedTuple` as a type,
they arguably shouldn't. Therefore, we outright ignore it and don't
touch or lint on it.
For a more detailed discussion, see the linked issue.
## Test Plan
Added examples to the existing tests.
## Related Issues
Fixes: https://github.com/astral-sh/ruff/issues/18619