Fix heap-use-after-free when converting scene group to global #25821

Job	Run time
📊 Static checks / Code style, file formatting, and docs	4m 50s
🍏 iOS / Template (target=template_release)	2m 32s
🤖 Android / Template (target=template_release)	29m 34s
🍎 macOS / Editor (target=editor, tests=yes)	25m 13s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	4m 45s
🍎 macOS / Template (target=template_release)	3m 10s
🏁 Windows / Editor (target=editor, tests=yes)	44m 21s
🌐 Web / Template w/o threads (target=template_release, threads=no)	4m 25s
🏁 Windows / Template (target=template_release)	31m 41s
🐧 Linux / Editor w/ Mono (target=editor)	38m 24s
🐧 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)	17m 44s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	7m 5s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	30m 9s
🐧 Linux / Template w/ Mono (target=template_release)	24m 17s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 8s
🪲 Godot CPP / Build and test Godot CPP	7m 27s
	4h 36m 45s

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