Use Never in more messages, use ambiguous in join #12492

Job	Run time
Test mypyc suite with 32-bit Python	7m 32s
Test mypyc suite with 32-bit Python	7m 32s
Test suite with py38-ubuntu, mypyc-compiled	17m 19s
Test suite with py38-ubuntu, mypyc-compiled	17m 19s
Test suite with py38-windows-64	20m 16s
Test suite with py38-windows-64	20m 16s
Test suite with py39-ubuntu	16m 31s
Test suite with py39-ubuntu	16m 31s
Test suite with py310-ubuntu	16m 1s
Test suite with py310-ubuntu	16m 1s
Test suite with py311-ubuntu, mypyc-compiled	16m 3s
Test suite with py311-ubuntu, mypyc-compiled	16m 3s
Test suite with py312-ubuntu, mypyc-compiled	17m 48s
Test suite with py312-ubuntu, mypyc-compiled	17m 48s
mypyc runtime tests with py39-macos	35s
mypyc runtime tests with py39-macos	4m 23s
mypyc runtime tests with py38-debug-build-ubuntu	4m 58s
mypyc runtime tests with py38-debug-build-ubuntu	4m 58s
Type check our own code (py38-ubuntu)	1m 44s
Type check our own code (py38-ubuntu)	1m 44s
Type check our own code (py38-windows-64)	2m 36s
Type check our own code (py38-windows-64)	2m 36s
Formatting and code style with Black + ruff	40s
Formatting and code style with Black + ruff	40s
	4h 7m 54s

Provide feedback