mypy

gh-127443: add tool for linting `Doc/data/refcounts.dat` #10946

Job	Run time
Run mypy on Lib/_pyrepl	1s
Run mypy on Lib/test/libregrtest	1s
Run mypy on Tools/build	1s
Run mypy on Tools/cases_generator	1s
Run mypy on Tools/clinic	1s
Run mypy on Tools/jit	1s
Run mypy on Tools/refcounts	1s
Run mypy on Tools/peg_generator	1s
Run mypy on Tools/wasm	1s
	9s

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