mypy

GH-139040: Add Dev Container instructions in JIT README (#139041) #16899

Job	Run time
Run mypy on Tools/build	19s
Run mypy on Lib/_pyrepl	17s
Run mypy on Lib/tomllib	19s
Run mypy on Tools/cases_generator	15s
Run mypy on Tools/clinic	21s
Run mypy on Tools/peg_generator	18s
Run mypy on Tools/jit	20s
Run mypy on Lib/test/libregrtest	20s
	2m 29s

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