Fixed duplicating nodes at different depths in SceneTreeDock #91

Job	Run time
📊 Static checks / Code style, file formatting, and docs	2m 22s
🍏 iOS / Template (target=template_release)	2m 46s
🤖 Android / Template (target=template_release)	3m 22s
🌐 Web / Template (target=template_release)	1m 7s
🍎 macOS / Editor (target=editor, tests=yes)	4m 26s
🐧 Linux / Editor w/ Mono (target=editor)	3m 13s
🍎 macOS / Template (target=template_release)	13m 57s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	11m 35s
🏁 Windows / Editor (target=editor, tests=yes)	6m 34s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	6m 34s
🏁 Windows / Template (target=template_release)	6m 0s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	7m 3s
🐧 Linux / Template w/ Mono (target=template_release)	1m 3s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 41s
🪲 Godot CPP / Build and test Godot CPP	6m 46s
	1h 18m 29s

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