mypy

gh-144264: Speed up Base64 decoding of data containing ignored charac… #19315

Job	Run time
Run mypy on Tools/build	24s
Run mypy on Lib/_pyrepl	20s
Run mypy on Lib/tomllib	15s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/clinic	21s
Run mypy on Tools/check-c-api-docs	16s
Run mypy on Tools/cases_generator	21s
Run mypy on Tools/jit	18s
Run mypy on Tools/peg_generator	23s
	2m 57s

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