Fix export variable of type Node pointing to a wrong child node when duplicating #14962

Job	Run time
📊 Static checks / Code style, file formatting, and docs	33s
🤖 Android / Template (target=template_release)	4m 22s
🍏 iOS / Template (target=template_release)	2m 11s
🍎 macOS / Editor (target=editor, tests=yes)	40m 16s
🌐 Web / Template (target=template_release)	1m 31s
🍎 macOS / Template (target=template_release)	28m 41s
🐧 Linux / Editor w/ Mono (target=editor)	5m 46s
🐧 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)	10m 20s
🏁 Windows / Editor (target=editor, tests=yes)	10m 26s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	8m 2s
🏁 Windows / Template (target=template_release)	9m 9s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	5m 36s
🐧 Linux / Template w/ Mono (target=template_release)	1m 0s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 3s
🪲 Godot CPP / Build and test Godot CPP	12m 38s
	2h 21m 34s

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