Fix Polygon2D to Skeleton2D transform calculation #586

Job	Run time
📊 Static checks / Code style, file formatting, and docs	3m 26s
🐧 Linux / Editor w/ Mono (target=editor)	25m 8s
🐧 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)	25m 34s
🤖 Android / Template (target=template_release)	15m 11s
🍏 iOS / Template (target=template_release)	21m 34s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	20m 21s
🍎 macOS / Editor (target=editor, tests=yes)	22m 56s
🍎 macOS / Template (target=template_release)	8m 8s
🐧 Linux / Template w/ Mono (target=template_release)	12m 43s
🌐 Web / Template (target=template_release)	9m 45s
🐧 Linux / Minimal template (target=template_release, everything disabled)	9m 18s
🏁 Windows / Editor (target=editor, tests=yes)	26m 45s
🏁 Windows / Template (target=template_release)	15m 34s
🪲 Godot CPP / Build and test Godot CPP	6m 50s
	3h 43m 13s

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