Improve `declare_class!` tests #2085

Job	Run time
Check formatting	10s
Check MSRV	2m 12s
Lint macOS 64bit	5m 41s
Lint iOS 32bit	1m 10s
Lint GNUStep + exceptions	2m 2s
Lint header-translator	57s
Lint test-assembly	42s
Assembly tests	7m 9s
Test macOS 12	6m 41s
Verify header translator output	1m 33s
Test Compiler-RT	37s
${{ matrix.name }}	0s
Check icrate features	0s
Test GNUStep with libobjc2 v1.9	3m 7s
Test GNUStep with libobjc2 v2.0	6m 8s
Test GNUStep with libobjc2 v2.1 on nightly	4m 27s
Test GNUStep 32bit	3m 38s
Compiler UI	1m 19s
Test on iOS simulator w. dinghy	0s
	47m 33s

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