Fix TypeIs for types with type params in Unions #12389

Job	Run time
Test mypyc suite with 32-bit Python	7m 28s
Test suite with py38-ubuntu, mypyc-compiled	17m 11s
Test suite with py38-windows-64	19m 19s
Test suite with py39-ubuntu	16m 31s
Test suite with py310-ubuntu	15m 7s
Test suite with py311-ubuntu, mypyc-compiled	15m 58s
Test suite with py312-ubuntu, mypyc-compiled	17m 36s
mypyc runtime tests with py39-macos	5m 35s
mypyc runtime tests with py38-debug-build-ubuntu	4m 40s
Type check our own code (py38-ubuntu)	1m 50s
Type check our own code (py38-windows-64)	2m 39s
Formatting and code style with Black + ruff	40s
	2h 4m 34s

Provide feedback