mypy

gh-134160: Start "Extending and embedding" with a Diataxis-style tuto… #18675

Job	Run time
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	18s
Run mypy on Lib/_pyrepl	17s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/clinic	17s
Run mypy on Tools/peg_generator	19s
Run mypy on Tools/jit	19s
Run mypy on Tools/check-c-api-docs	15s
Run mypy on Tools/cases_generator	16s
	2m 34s

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