mypy

gh-144822: remove redundant decref in `codegen.c` (#144823) #19530

Job	Run time
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/check-c-api-docs	19s
Run mypy on Tools/cases_generator	17s
Run mypy on Lib/tomllib	16s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/clinic	18s
Run mypy on Tools/build	15s
Run mypy on Tools/jit	20s
Run mypy on Tools/peg_generator	19s
	2m 42s

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