mypy

gh-140814: Fix freeze_support() setting start method as side effect (… #19970

Job	Run time
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/build	19s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/check-c-api-docs	18s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/clinic	17s
Run mypy on Lib/_pyrepl	20s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/jit	18s
	2m 48s

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