Tests

Fix slots issue with deferred base #20092

Job	Run time
Test mypyc suite with 32-bit Python	30s
Test suite with py312-ubuntu	31s
Test suite with py311-ubuntu	16s
Test suite with py314t-ubuntu, mypyc-compiled	21s
Test suite with py310-ubuntu, mypyc-compiled	32s
Test suite with py313-ubuntu, mypyc-compiled	32s
Formatting and code style with Black + ruff	31s
Type check our own code (py310-windows-64)	28s
mypyc runtime tests with py313-macos	31s
Parallel tests with py314-ubuntu, interpreted	32s
Parallel tests with py314-ubuntu, mypyc-compiled	23s
mypyc runtime tests with py310-ubuntu	28s
Test suite with py314-windows-64	21s
Type check our own code (py310-ubuntu)	27s
Test suite with py314-ubuntu, mypyc-compiled	31s
	6m 54s

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