Split CopyOrMutCopy retain semantics in two #3124

Job	Run time
Check MSRV	47s
Check formatting	11s
Lint macOS x86_64	2m 32s
Lint iOS ARMv7s	2m 27s
Lint visionOS Aarch64 simulator	2m 19s
Lint GNUStep + exceptions	1m 28s
Lint header-translator	28s
Lint test-assembly	31s
Test macOS 15 Aarch64	1m 21s
Verify header translator output	52s
Compiler UI	46s
Assembly tests	49s
Check framework features	0s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test Compiler-RT	27s
Test GNUStep with libobjc2 v1.9	1m 3s
Test GNUStep with libobjc2 v2.0	1m 18s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.1 on nightly	59s
Test GNUStep 32bit	1m 14s
	19m 32s

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