mypy

gh-139227: Remove unused _PyRuntime.imports.pkgcontext (#151490) #21908

Job	Run time
Run mypy on Tools/cases_generator	20s
Run mypy on Tools/check-c-api-docs	13s
Run mypy on Lib/test/libregrtest	17s
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/peg_generator	19s
Run mypy on Lib/tomllib	19s
Run mypy on Tools/build	18s
Run mypy on Tools/jit	21s
Run mypy on Tools/clinic	21s
	2m 49s

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