mypy

gh-148788: Update Emscripten example post move to Platforms dir (#148… #20797

Job	Run time
Run mypy on Lib/_pyrepl	18s
Run mypy on Tools/clinic	18s
Run mypy on Tools/jit	16s
Run mypy on Tools/cases_generator	17s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/peg_generator	21s
Run mypy on Tools/check-c-api-docs	16s
Run mypy on Tools/build	19s
	2m 40s

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