mypy

gh-82665 Mention that HTMLParser.handle_starttag value can be None (#… #20901

Job	Run time
Run mypy on Tools/cases_generator	19s
Run mypy on Tools/clinic	16s
Run mypy on Lib/tomllib	20s
Run mypy on Lib/_pyrepl	26s
Run mypy on Tools/check-c-api-docs	15s
Run mypy on Tools/build	17s
Run mypy on Lib/test/libregrtest	16s
Run mypy on Tools/peg_generator	22s
Run mypy on Tools/jit	18s
	2m 49s

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