Fix Rust panics in `exception::catch`, and make it safe #3111

Job	Run time
Check MSRV	51s
Check formatting	10s
Lint macOS x86_64	2m 35s
Lint iOS ARMv7s	2m 23s
Lint visionOS Aarch64 simulator	2m 23s
Lint GNUStep + exceptions	1m 16s
Lint header-translator	29s
Lint test-assembly	30s
Test macOS 15 Aarch64	1m 21s
Verify header translator output	55s
Assembly tests	50s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Check framework features	0s
Test Compiler-RT	38s
Test GNUStep with libobjc2 v1.9	1m 23s
Compiler UI	44s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.0	58s
Test GNUStep with libobjc2 v2.1 on nightly	1m 7s
Test GNUStep 32bit	1m 46s
	20m 19s

Provide feedback