chore: Add mypy github action

[TrevorBergeron]

Fixes: b/401037761

[tswast]

Do we actually want this one? As far as I know GitHub won't commit the changes back. lint also runs the formatter but will fail if any makes a change.

[TrevorBergeron]

I was just being conservative, and assumed that format checked things that lint didn't. So to be clear, we don't need format as a prerelease check at all?

[TrevorBergeron]

ok, so it looks like lint wasn't doing isort, so I integrated isort --check into the lint workflow, so no need for format

[tswast]

If we add this here, I think we can safely remove from

python-bigquery-dataframes/noxfile.py

Line 119 in 7b0cab5

"mypy",

which defines the list used in the kokoro presubmit. Or are you waiting to do that cleanup in a subsequent PR (once mypy is required check, perhaps?)

[TrevorBergeron]

Removing it (and others) in a following PR: #1459.

[tswast]

I think we can remove this file now that lint runs both black and isort.

[TrevorBergeron]

removed