Tests

Use Never in more messages, use ambiguous in join (#17304) #433

Job	Run time
Test mypyc suite with 32-bit Python	7m 16s
Test suite with py38-ubuntu, mypyc-compiled	17m 26s
Test suite with py38-windows-64	20m 28s
Test suite with py39-ubuntu	16m 36s
Test suite with py310-ubuntu	16m 7s
Test suite with py311-ubuntu, mypyc-compiled	15m 46s
Test suite with py312-ubuntu, mypyc-compiled	18m 28s
mypyc runtime tests with py39-macos	4m 42s
mypyc runtime tests with py38-debug-build-ubuntu	4m 36s
Type check our own code (py38-ubuntu)	1m 46s
Type check our own code (py38-windows-64)	2m 38s
Formatting and code style with Black + ruff	40s
	2h 6m 29s

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