mypy

gh-129889: Support context manager protocol by contextvars.Token (#12… #52

Job	Run time
Run mypy on Lib/_pyrepl	17s
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/build	15s
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/clinic	18s
Run mypy on Tools/jit	23s
Run mypy on Tools/peg_generator	15s
Run mypy on Tools/wasm	16s
	2m 21s

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