TST: Localize warning ignore in typestubs_for_units.py #18567

I worry that a global ignore here is going to change the warning state for unrelated tests in the test run.

Desired outcome: Localize the warning ignore using context manager to only where it is really needed, or exclude the problematic "deprecated.py" and not use any ignore at all.

This is caused by:

• Add script to make type stub for units #18547