Tests

Rework starargs with union argument #17360

Job	Run time
Test mypyc suite with 32-bit Python	12m 31s
Test suite with py39-ubuntu, mypyc-compiled	14m 41s
Test suite with py312-ubuntu, mypyc-compiled	13m 18s
Test suite with py311-ubuntu	8m 38s
Test suite with py310-ubuntu	11m 26s
Test suite with py314-dev-ubuntu	15m 12s
Test suite with py313-ubuntu, mypyc-compiled	12m 54s
Type check our own code (py39-ubuntu)	1m 41s
Formatting and code style with Black + ruff	1m 50s
mypyc runtime tests with py39-macos	6m 59s
Test suite with py313-windows-64	22m 31s
Type check our own code (py39-windows-64)	2m 10s
	2h 3m 51s

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