Tests

Revert dict.or typeshed change #21578

Job	Run time
Test mypyc suite with 32-bit Python	11m 15s
Test suite with py313-ubuntu, mypyc-compiled	16m 26s
Test suite with py314-ubuntu, mypyc-compiled	16m 21s
Test suite with py310-ubuntu, mypyc-compiled	16m 48s
Test suite with py311-ubuntu	9m 36s
Test suite with py312-ubuntu	10m 36s
Test suite with py314t-ubuntu, mypyc-compiled	18m 20s
Test suite with py314-windows-64	29m 13s
Formatting and code style with Black + ruff	1m 53s
mypyc runtime tests with py313-macos	5m 36s
Type check our own code (py310-windows-64)	2m 24s
mypyc runtime tests with py310-ubuntu	6m 18s
Parallel tests with py314-windows-64, interpreted	11m 35s
Parallel tests with py314-ubuntu, mypyc-compiled	24m 4s
Type check our own code (py310-ubuntu)	1m 35s
Parallel tests with py314-ubuntu, interpreted	25m 20s
	3h 27m 20s

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