[mypyc] Show traceback when emitfunc unit test fails #12405

Job	Run time
Test suite with py38-ubuntu, mypyc-compiled	17m 5s
Test suite with py38-windows-64	19m 44s
Test suite with py39-ubuntu	16m 19s
Test mypyc suite with 32-bit Python	7m 26s
Test suite with py310-ubuntu	15m 55s
Test suite with py311-ubuntu, mypyc-compiled	15m 17s
Test suite with py312-ubuntu, mypyc-compiled	17m 11s
mypyc runtime tests with py39-macos	4m 17s
mypyc runtime tests with py38-debug-build-ubuntu	4m 29s
Type check our own code (py38-ubuntu)	2m 2s
Type check our own code (py38-windows-64)	2m 54s
Formatting and code style with Black + ruff	36s
	2h 3m 15s

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