mypy

Indexing is more straight-forward (and faster) than unpacking (gh-145… #19660

Job	Run time
Run mypy on Lib/tomllib	17s
Run mypy on Tools/peg_generator	17s
Run mypy on Tools/check-c-api-docs	19s
Run mypy on Tools/build	15s
Run mypy on Tools/jit	17s
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/clinic	20s
Run mypy on Tools/cases_generator	18s
Run mypy on Lib/test/libregrtest	23s
	2m 47s

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