Tests

Mention what codes are actually ignored in `not covered by "type: ignore" comment` note #18330

Job	Run time
Test mypyc suite with 32-bit Python	9m 51s
Test suite with py311-ubuntu	8m 26s
Test suite with py310-ubuntu	10m 41s
Test suite with py312-ubuntu, mypyc-compiled	13m 13s
Test suite with py313-windows-64	25m 32s
Test suite with py39-ubuntu, mypyc-compiled	15m 3s
mypyc runtime tests with py39-macos	7m 21s
Test suite with py313-ubuntu, mypyc-compiled	13m 15s
Test suite with py314-dev-ubuntu	16m 19s
Type check our own code (py39-ubuntu)	1m 41s
Formatting and code style with Black + ruff	1m 47s
Type check our own code (py39-windows-64)	2m 8s
	2h 5m 17s

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