mypy

gh-133879: Copyedit "What's new in Python 3.15" (#148686) #20794

Job	Run time
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/check-c-api-docs	19s
Run mypy on Tools/cases_generator	20s
Run mypy on Lib/_pyrepl	17s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/jit	17s
Run mypy on Tools/peg_generator	17s
Run mypy on Tools/clinic	15s
	2m 37s

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