mypy

gh-145000: find correct merge base in check-html-ids #20320

Job	Run time
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/clinic	19s
Run mypy on Tools/build	19s
Run mypy on Tools/jit	18s
Run mypy on Tools/check-c-api-docs	18s
Run mypy on Lib/tomllib	12s
Run mypy on Tools/cases_generator	20s
Run mypy on Lib/_pyrepl	17s
Run mypy on Tools/peg_generator	17s
	2m 38s

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