Stubtest: ignore `_ios_support` #12423

Job	Run time
Test mypyc suite with 32-bit Python	7m 56s
Test suite with py38-ubuntu, mypyc-compiled	17m 7s
Test suite with py38-windows-64	20m 12s
Test suite with py39-ubuntu	16m 20s
Test suite with py310-ubuntu	15m 19s
Test suite with py311-ubuntu, mypyc-compiled	15m 46s
Test suite with py312-ubuntu, mypyc-compiled	17m 31s
mypyc runtime tests with py39-macos	5m 41s
mypyc runtime tests with py38-debug-build-ubuntu	4m 32s
Type check our own code (py38-ubuntu)	1m 49s
Type check our own code (py38-windows-64)	2m 25s
Formatting and code style with Black + ruff	36s
	2h 5m 14s

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