mypy

gh-140578: Doc: Remove sencence implying that concurrent.futures.Thre… #17828

Job	Run time
Run mypy on Tools/cases_generator	13s
Run mypy on Tools/build	21s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/clinic	16s
Run mypy on Tools/jit	17s
Run mypy on Lib/_pyrepl	12s
Run mypy on Tools/peg_generator	11s
	2m 5s

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