mypy

gh-111501: venv: do not export PS1 in activate (#105279) #22023

Job	Run time
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/clinic	19s
Run mypy on Tools/jit	19s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Tools/cases_generator	18s
Run mypy on Tools/peg_generator	18s
Run mypy on Tools/build	19s
Run mypy on Lib/tomllib	20s
Run mypy on Lib/test/libregrtest	23s
	2m 52s

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