mypy

gh-148726: Add gc changes to What's New (#149398) #21151

Job	Run time
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/jit	15s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Tools/build	14s
Run mypy on Tools/cases_generator	14s
Run mypy on Lib/tomllib	12s
Run mypy on Tools/clinic	19s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/peg_generator	14s
	2m 25s

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