Update to Xcode 16 #3050

Job	Run time
Check formatting	15s
Lint macOS 64bit	2m 51s
Check MSRV	55s
Lint iOS 32bit	2m 17s
Lint GNUStep + exceptions	1m 31s
Lint header-translator	33s
Lint test-assembly	28s
Test macOS 12	3m 27s
Verify header translator output	58s
Assembly tests	49s
Check framework features	0s
${{ matrix.name }}	0s
Test Compiler-RT	27s
Test GNUStep with libobjc2 v1.9	1m 10s
Compiler UI	1m 51s
Test GNUStep with libobjc2 v2.0	1m 17s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.1 on nightly	58s
Test GNUStep 32bit	1m 25s
	21m 12s

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