mypy

gh-138451: Support custom LLVM installation path #16530

Job	Run time
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/clinic	15s
Run mypy on Lib/tomllib	24s
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	22s
Run mypy on Tools/cases_generator	15s
Run mypy on Tools/jit	13s
Run mypy on Tools/peg_generator	19s
	2m 26s

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