mypy

gh-140734: fix off-by-one error when comparing to `_SUN_PATH_MAX` (#1… #17758

Job	Run time
Run mypy on Lib/_pyrepl	18s
Run mypy on Tools/jit	21s
Run mypy on Lib/tomllib	14s
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/clinic	20s
Run mypy on Tools/build	21s
Run mypy on Tools/cases_generator	21s
Run mypy on Tools/peg_generator	20s
	2m 33s

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