mypy

gh-133879: Clean up What's New for 3.15 (#140435) #17657

Job	Run time
Run mypy on Tools/clinic	26s
Run mypy on Tools/cases_generator	21s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Lib/tomllib	19s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/jit	22s
	2m 44s

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