Fix `SoftBody3D` for double-precision builds #22779

Job	Run time
📊 Static checks / Code style, file formatting, and docs	35s
🍏 iOS / Template (target=template_release)	27m 20s
🤖 Android / Template (target=template_release)	30m 6s
🍎 macOS / Editor (target=editor, tests=yes)	28m 50s
🐧 Linux / Editor w/ Mono (target=editor)	37m 12s
🍎 macOS / Template (target=template_release)	24m 44s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	4m 27s
🏁 Windows / Editor (target=editor, tests=yes)	42m 32s
🌐 Web / Template w/o threads (target=template_release, threads=no)	4m 39s
🐧 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)	36m 0s
🏁 Windows / Template (target=template_release)	29m 54s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	32m 18s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	28m 40s
🐧 Linux / Template w/ Mono (target=template_release)	23m 57s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 45s
🪲 Godot CPP / Build and test Godot CPP	6m 38s
	6h 12m 37s

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