mypy

gh-143700: document `secrets.DEFAULT_ENTROPY` as an opaque value (#14… #19428

Job	Run time
Run mypy on Lib/tomllib	19s
Run mypy on Tools/peg_generator	19s
Run mypy on Tools/check-c-api-docs	20s
Run mypy on Tools/clinic	17s
Run mypy on Tools/jit	21s
Run mypy on Lib/test/libregrtest	21s
Run mypy on Tools/cases_generator	15s
Run mypy on Tools/build	17s
Run mypy on Lib/_pyrepl	19s
	2m 48s

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