mypy

gh-138451: Support custom LLVM installation path (#138452) #20808

Job	Run time
Run mypy on Tools/cases_generator	20s
Run mypy on Tools/check-c-api-docs	20s
Run mypy on Tools/clinic	16s
Run mypy on Lib/_pyrepl	20s
Run mypy on Tools/jit	14s
Run mypy on Lib/tomllib	19s
Run mypy on Tools/build	14s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/peg_generator	18s
	2m 41s

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