mypy

gh-148814: Fix an issue in Emscripten README (#148752) #20812

Job	Run time
Run mypy on Lib/_pyrepl	20s
Run mypy on Tools/build	18s
Run mypy on Lib/tomllib	14s
Run mypy on Lib/test/libregrtest	17s
Run mypy on Tools/peg_generator	19s
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/check-c-api-docs	16s
Run mypy on Tools/jit	20s
Run mypy on Tools/clinic	20s
	2m 43s

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