Fix Skeleton2D.{_set|_get} always returning true #162

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 3s
🍏 iOS / Template (target=template_release)	9m 13s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	25m 31s
🤖 Android / Editor (target=editor)	24m 13s
🐧 Linux / Editor w/ Mono (target=editor)	41m 28s
🌐 Web / Template w/o threads (target=template_release, threads=no)	26m 17s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	16m 18s
🐧 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)	46m 21s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	16m 50s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	39m 17s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	31m 55s
🍎 macOS / Editor (target=editor, tests=yes)	28m 44s
🐧 Linux / Template w/ Mono (target=template_release)	27m 29s
🏁 Windows / Editor (target=editor, tests=yes)	47m 57s
🍎 macOS / Template (target=template_release)	20m 47s
🐧 Linux / Minimal template (target=template_release, everything disabled)	16m 16s
🏁 Windows / Template (target=template_release)	35m 4s
🪲 Godot CPP / Build and test Godot CPP	8m 6s
	7h 42m 49s

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