[mypyc] Show traceback when emitfunc unit test fails (#17262) #12409

Job	Run time
Test mypyc suite with 32-bit Python	7m 53s
Test suite with py38-ubuntu, mypyc-compiled	17m 23s
Test suite with py38-windows-64	20m 12s
Test suite with py39-ubuntu	16m 11s
Test suite with py310-ubuntu	15m 21s
Test suite with py311-ubuntu, mypyc-compiled	15m 35s
Test suite with py312-ubuntu, mypyc-compiled	17m 10s
mypyc runtime tests with py39-macos	4m 29s
mypyc runtime tests with py38-debug-build-ubuntu	5m 38s
Type check our own code (py38-ubuntu)	1m 50s
Type check our own code (py38-windows-64)	2m 14s
Formatting and code style with Black + ruff	37s
	2h 4m 33s

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