[WIP] Async Signals #3369

Job	Run time
license-guard	34s
run-examples	1m 24s
godot-itest (macos)	15m 15s
clippy	1m 41s
godot-itest (windows)	15m 8s
rustfmt	22s
godot-itest (linux-full)	15m 16s
godot-itest (linux-features-experimental)	15m 14s
doc-lints	40s
godot-itest (linux-4.1)	1m 9s
unit-test	2m 13s
godot-itest (linux-4.2)	15m 14s
godot-itest (linux-4.3)	15m 16s
godot-itest (linux-memcheck)	15m 15s
ci-status	4s
	1h 54m 45s

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