mypy

gh-141004: Add a CI job ensuring that new C APIs include documentatio… #18238

Job	Run time
Run mypy on Tools/build	18s
Run mypy on Tools/clinic	19s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/jit	20s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/peg_generator	21s
Run mypy on Lib/_pyrepl	19s
	2m 33s

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