mypy

gh-91048: Fix external inspection multi-threaded performance (#136005) #15509

Job	Run time
Run mypy on Tools/build	21s
Run mypy on Lib/_pyrepl	20s
Run mypy on Lib/tomllib	20s
Run mypy on Tools/cases_generator	21s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/clinic	21s
Run mypy on Tools/jit	19s
Run mypy on Tools/peg_generator	18s
	2m 40s

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