mypy

gh-138577: Mention Unix-specific limitations of `getpass.getpass(echo… #9577

Job	Run time
Run mypy on Lib/test/libregrtest	15s
Run mypy on Lib/_pyrepl	18s
Run mypy on Lib/tomllib	13s
Run mypy on Tools/clinic	23s
Run mypy on Tools/build	22s
Run mypy on Tools/jit	16s
Run mypy on Tools/cases_generator	17s
Run mypy on Tools/peg_generator	20s
	2m 24s

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