mypy

gh-118150: warn in doc about results asymmetry for difflib junk (GH-1… #22774

Job	Run time
Run mypy on Tools/cases_generator	31s
Run mypy on Tools/check-c-api-docs	33s
Run mypy on Tools/build	31s
Run mypy on Tools/jit	36s
Run mypy on Lib/_pyrepl	34s
Run mypy on Lib/test/libregrtest	33s
Run mypy on Tools/clinic	32s
Run mypy on Lib/tomllib	29s
Run mypy on Tools/peg_generator	35s
	4m 54s

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