mypy

gh-133879: Copyedit "What's new in Python 3.15" (#146345) #20140

Job	Run time
Run mypy on Tools/clinic	19s
Run mypy on Tools/build	18s
Run mypy on Tools/cases_generator	17s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/peg_generator	19s
Run mypy on Lib/_pyrepl	24s
Run mypy on Tools/jit	19s
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/check-c-api-docs	18s
	2m 49s

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