mypy

GH-132042: Fix calculation of slotdef index in update_one_slot() (#14… #19918

Job	Run time
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/check-c-api-docs	20s
Run mypy on Tools/jit	31s
Run mypy on Tools/peg_generator	19s
Run mypy on Tools/clinic	15s
Run mypy on Tools/cases_generator	24s
Run mypy on Lib/_pyrepl	23s
Run mypy on Lib/tomllib	15s
Run mypy on Tools/build	20s
	3m 7s

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