Fix TypeIs for types with type params in Unions #12373

Job	Run time
Test mypyc suite with 32-bit Python	7m 8s
Test suite with py38-ubuntu, mypyc-compiled	17m 58s
Test suite with py38-windows-64	19m 47s
Test suite with py39-ubuntu	16m 51s
Test suite with py310-ubuntu	15m 8s
Test suite with py311-ubuntu, mypyc-compiled	15m 6s
Test suite with py312-ubuntu, mypyc-compiled	17m 22s
mypyc runtime tests with py39-macos	4m 33s
mypyc runtime tests with py38-debug-build-ubuntu	4m 26s
Type check our own code (py38-ubuntu)	1m 46s
Type check our own code (py38-windows-64)	2m 26s
Formatting and code style with Black + ruff	39s
	2h 3m 10s

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