mypy

gh-85792: Update shebang to python3 #12757

Job	Run time
Run mypy on Lib/_pyrepl	14s
Run mypy on Lib/test/libregrtest	14s
Run mypy on Tools/build	16s
Run mypy on Tools/cases_generator	14s
Run mypy on Tools/clinic	14s
Run mypy on Tools/jit	17s
Run mypy on Tools/peg_generator	17s
Run mypy on Tools/wasm	15s
	2m 1s

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