mypy

gh-140476: optimize `PySet_Add` for `frozenset` in free-threading (#1… #17847

Job	Run time
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/build	19s
Run mypy on Lib/tomllib	18s
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/jit	22s
Run mypy on Lib/test/libregrtest	22s
Run mypy on Tools/peg_generator	15s
Run mypy on Tools/clinic	21s
	2m 37s

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