mypy

gh-101100: Fix Sphinx warnings in 'Buffer Object Structures' document… #21771

Job	Run time
Run mypy on Lib/test/libregrtest	19s
Run mypy on Lib/_pyrepl	17s
Run mypy on Tools/build	18s
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/check-c-api-docs	16s
Run mypy on Tools/peg_generator	23s
Run mypy on Tools/clinic	17s
Run mypy on Tools/jit	18s
Run mypy on Lib/tomllib	16s
	2m 43s

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