mypy

gh-148814: Fix an issue in Emscripten README (#148752) #10453

Job	Run time
Run mypy on Lib/test/libregrtest	24s
Run mypy on Tools/check-c-api-docs	18s
Run mypy on Lib/_pyrepl	18s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/build	16s
Run mypy on Tools/cases_generator	17s
Run mypy on Tools/peg_generator	16s
Run mypy on Tools/jit	15s
Run mypy on Tools/clinic	20s
	2m 41s

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