Fix theme StyleBox override parameter completion #30897

Job	Run time
📊 Static checks / Code style, file formatting, and docs	24s
🍎 macOS / Editor (target=editor, tests=yes)	4m 38s
🍎 macOS / Template (target=template_release)	3m 0s
🤖 Android / Template (target=template_release)	4m 36s
🐧 Linux / Editor w/ Mono (target=editor)	4m 43s
🐧 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)	19m 37s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	6m 49s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	7m 23s
🍏 iOS / Template (target=template_release)	1m 49s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	4m 1s
🐧 Linux / Template w/ Mono (target=template_release)	2m 53s
🌐 Web / Template w/o threads (target=template_release, threads=no)	4m 12s
🐧 Linux / Minimal template (target=template_release, everything disabled)	2m 6s
🏁 Windows / Editor (target=editor, tests=yes)	10m 45s
🏁 Windows / Template (target=template_release)	8m 40s
🪲 Godot CPP / Build and test Godot CPP	6m 44s
	1h 32m 20s

Provide feedback