mypy

gh-145623: Fix crashes on uninitialized struct.Struct objects (gh-145… #19820

Job	Run time
Run mypy on Tools/cases_generator	20s
Run mypy on Tools/check-c-api-docs	16s
Run mypy on Lib/test/libregrtest	20s
Run mypy on Tools/build	17s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/jit	17s
Run mypy on Tools/peg_generator	18s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/clinic	18s
	2m 42s

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