mypy

Doc: remove duplicate GitHub issue reference in "What's New in Python… #19001

Job	Run time
Run mypy on Tools/cases_generator	18s
Run mypy on Lib/test/libregrtest	21s
Run mypy on Tools/jit	19s
Run mypy on Tools/clinic	18s
Run mypy on Lib/tomllib	19s
Run mypy on Tools/peg_generator	19s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/build	17s
Run mypy on Tools/check-c-api-docs	21s
	2m 51s

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