Fix Rust panics in `exception::catch`, and make it safe #3106

Job	Run time
Check formatting	12s
Lint macOS x86_64	2m 39s
Check MSRV	45s
Lint iOS ARMv7s	2m 24s
Lint visionOS Aarch64 simulator	2m 25s
Lint GNUStep + exceptions	1m 25s
Lint header-translator	29s
Lint test-assembly	29s
Test macOS 15 Aarch64	1m 35s
Verify header translator output	1m 17s
Test Compiler-RT	1m 9s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Assembly tests	1m 3s
Check framework features	0s
Test on iOS simulator w. dinghy	0s
Compiler UI	49s
Test GNUStep with libobjc2 v1.9	1m 13s
Test GNUStep with libobjc2 v2.0	1m 17s
Test GNUStep with libobjc2 v2.1 on nightly	58s
Test GNUStep 32bit	1m 14s
	21m 23s

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