Fix auto traits for custom classes subclassing NSObject #3144

Job	Run time
Lint macOS x86_64	2m 27s
Check formatting	7s
Check MSRV	43s
Lint iOS ARMv7s	2m 24s
Lint visionOS Aarch64 simulator	2m 22s
Lint GNUStep + exceptions	1m 22s
Lint header-translator	29s
Lint test-assembly	25s
Test macOS 15 Aarch64	1m 17s
Assembly tests	53s
Verify header translator output	52s
Check framework features	0s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test Compiler-RT	25s
Test GNUStep with libobjc2 v1.9	1m 1s
Test on iOS simulator w. dinghy	0s
Compiler UI	43s
Test GNUStep with libobjc2 v2.0	1m 18s
Test GNUStep with libobjc2 v2.1 on nightly	1m 16s
Test GNUStep 32bit	1m 6s
	19m 10s

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