Fix tests on macOS 10.12 #3082

Job	Run time
Check formatting	23s
Lint macOS 64bit	2m 42s
Check MSRV	51s
Lint iOS 32bit	2m 6s
Lint GNUStep + exceptions	1m 28s
Lint header-translator	27s
Lint test-assembly	24s
Test macOS 12	2m 39s
Verify header translator output	8s
Assembly tests	47s
Compiler UI	1m 55s
Test Compiler-RT	51s
${{ matrix.name }}	0s
Check framework features	0s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v1.9	1m 50s
Test GNUStep with libobjc2 v2.0	1m 12s
Test GNUStep with libobjc2 v2.1 on nightly	1m 17s
Test GNUStep 32bit	1m 11s
	20m 11s

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