Tests

Add more test cases for type narrowing #20364

Job	Run time
Test mypyc suite with 32-bit Python	9m 33s
Test suite with py310-ubuntu, mypyc-compiled	14m 43s
Type check our own code (py310-ubuntu)	1m 43s
Test suite with py314-windows-64	27m 5s
Parallel tests with py314-ubuntu, interpreted	25m 30s
Test suite with py311-ubuntu	9m 41s
Test suite with py314t-ubuntu, mypyc-compiled	17m 38s
Test suite with py314-ubuntu, mypyc-compiled	14m 49s
mypyc runtime tests with py313-macos	5m 8s
mypyc runtime tests with py310-ubuntu	5m 20s
Test suite with py313-ubuntu, mypyc-compiled	15m 33s
Type check our own code (py310-windows-64)	2m 16s
Test suite with py312-ubuntu	10m 16s
Formatting and code style with Black + ruff	1m 59s
Parallel tests with py314-ubuntu, mypyc-compiled	28m 36s
	3h 9m 50s

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