Tests

Fix various test flakiness on Windows #21715

Job	Run time
Test mypyc suite with 32-bit Python	10m 52s
Test suite with py312-ubuntu	9m 16s
Parallel tests with py314-ubuntu, interpreted	24m 13s
mypyc runtime tests with py313-macos	7m 0s
Test suite with py314-ubuntu, mypyc-compiled	15m 8s
Test suite with py313-ubuntu, mypyc-compiled	15m 36s
Parallel tests with py314-ubuntu, mypyc-compiled	25m 2s
Test suite with py311-ubuntu	8m 39s
Type check our own code (py310-windows-64)	2m 16s
Parallel tests with py314-windows-64, interpreted	5m 46s
Formatting and code style with Black + ruff	1m 53s
mypyc runtime tests with py310-ubuntu	6m 46s
Type check our own code (py310-ubuntu)	1m 45s
Test suite with py310-ubuntu, mypyc-compiled	16m 25s
Test suite with py314-windows-64	25m 19s
Test suite with py314t-ubuntu, mypyc-compiled	17m 34s
	3h 13m 30s

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