mypy

gh-142440: Fix _decimal builds configured with EXTRA_FUNCTIONALITY (G… #19167

Job	Run time
Run mypy on Lib/_pyrepl	17s
Run mypy on Tools/jit	22s
Run mypy on Tools/build	19s
Run mypy on Tools/cases_generator	19s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/check-c-api-docs	19s
Run mypy on Lib/test/libregrtest	24s
Run mypy on Tools/clinic	18s
Run mypy on Tools/peg_generator	17s
	2m 51s

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