gh-119993 ignore `NotADirectoryError` in `Path.unlink()` if `missing_ok` is `True`

[MusicalNinjaDad]

Add a short note on when Path.unlink() raises NotADirectoryError

This can occur "in the wild", for example, after calling shutil.move(src, dst) where dst is a non-existent directory. Debugging can cost a lot of time as the cause can be non-intuitive, potentially not nearby in the code and the docs don't mention the exception as being raised in any circumstances. (This just happened to me after encountering pypa/cibuildwheel#1850)

Fixes: #119993

• Issue: gh-119993

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