Fix main thread requirements on protocols #2230

Job	Run time
Check formatting	9s
Lint macOS 64bit	3m 21s
Lint iOS 32bit	1m 15s
Lint GNUStep + exceptions	1m 39s
Lint header-translator	34s
Lint test-assembly	32s
Check MSRV	1m 4s
Test macOS 12	2m 15s
Check icrate features	0s
Compiler UI	0s
Verify header translator output	0s
Assembly tests	0s
${{ matrix.name }}	0s
Test Compiler-RT	0s
${{ matrix.name }}	0s
Test on iOS simulator w. dinghy	0s
	10m 49s

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