Panic handling: thread safety; set hook once and not repeatedly #3350

Job	Run time
doc-lints	41s
godot-itest (macos)	35s
clippy	42s
godot-itest (windows)	34s
license-guard	31s
godot-itest (linux-full)	31s
run-examples	40s
godot-itest (linux-features-experimental)	43s
godot-itest (linux-4.1)	42s
rustfmt	10s
unit-test	40s
godot-itest (linux-4.2)	30s
godot-itest (linux-4.3)	42s
godot-itest (linux-memcheck)	33s
ci-status	1s
	8m 15s

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