`Callable` is now passed by-ref #2946

Job	Run time
doc-lints	50s
rustfmt	26s
clippy	1m 25s
run-examples	47s
godot-itest (macos)	1m 28s
godot-itest (windows)	2m 25s
unit-test	1m 54s
godot-itest (linux-full)	2m 23s
godot-itest (linux-features-experimental)	2m 24s
godot-itest (linux-4.1)	1m 16s
godot-itest (linux-4.2)	1m 14s
license-guard	34s
godot-itest (linux-memcheck)	2m 26s
ci-status	1s
	19m 33s

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