mypy

Prevent GitHub's web conflict editor from converting LF to CRLF (#148… #10446

Job	Run time
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/check-c-api-docs	18s
Run mypy on Lib/_pyrepl	21s
Run mypy on Lib/tomllib	20s
Run mypy on Tools/build	17s
Run mypy on Tools/jit	17s
Run mypy on Tools/cases_generator	15s
Run mypy on Tools/peg_generator	18s
Run mypy on Tools/clinic	18s
	2m 44s

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