mypy

gh-140729: Fix subprocess handling in test_process_pool_executor_pick… #18019

Job	Run time
Run mypy on Lib/_pyrepl	22s
Run mypy on Lib/test/libregrtest	26s
Run mypy on Tools/build	19s
Run mypy on Tools/cases_generator	17s
Run mypy on Tools/clinic	19s
Run mypy on Tools/jit	20s
Run mypy on Tools/peg_generator	19s
Run mypy on Lib/tomllib	21s
	2m 43s

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