mypy

gh-144969: Document that the free threading GC can change ob_tid (#14… #19585

Job	Run time
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/peg_generator	18s
Run mypy on Lib/_pyrepl	18s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Tools/clinic	27s
Run mypy on Tools/build	20s
Run mypy on Tools/jit	16s
Run mypy on Tools/cases_generator	17s
Run mypy on Lib/tomllib	18s
	2m 49s

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