mypy

gh-150285: Fix too long docstrings in GenericAlias and __class_getite… #21857

Job	Run time
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	21s
Run mypy on Tools/peg_generator	17s
Run mypy on Tools/clinic	18s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Lib/tomllib	20s
Run mypy on Tools/jit	23s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/cases_generator	18s
	2m 50s

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