Tests

Prevent assignment to None for non-Optional class variables #20210

Job	Run time
Test mypyc suite with 32-bit Python	9m 26s
Test suite with py314t-ubuntu, mypyc-compiled	16m 59s
Test suite with py313-ubuntu, mypyc-compiled	15m 12s
Test suite with py311-ubuntu	9m 38s
Type check our own code (py310-windows-64)	2m 45s
Test suite with py314-ubuntu, mypyc-compiled	15m 7s
mypyc runtime tests with py310-ubuntu	5m 29s
Test suite with py312-ubuntu	10m 11s
Test suite with py314-windows-64	27m 52s
Type check our own code (py310-ubuntu)	1m 28s
Parallel tests with py314-ubuntu, interpreted	24m 31s
Parallel tests with py314-ubuntu, mypyc-compiled	27m 54s
Test suite with py310-ubuntu, mypyc-compiled	15m 11s
mypyc runtime tests with py313-macos	6m 16s
Formatting and code style with Black + ruff	2m 4s
	3h 10m 3s

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