Fix SpinBox will reset unsubmitted text when redrawing #13039

Job	Run time
📊 Static checks / Code style, file formatting, and docs	57s
🍎 macOS / Editor (target=editor, tests=yes)	43m 35s
🐧 Linux / Editor w/ Mono (target=editor)	51m 9s
🍎 macOS / Template (target=template_release)	14m 31s
🐧 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)	57m 58s
🤖 Android / Template (target=template_release)	58m 5s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	56m 38s
🍏 iOS / Template (target=template_release)	29m 10s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	35m 21s
🐧 Linux / Template w/ Mono (target=template_release)	33m 38s
🌐 Web / Template (target=template_release)	25m 57s
🐧 Linux / Minimal template (target=template_release, everything disabled)	20m 29s
🏁 Windows / Editor (target=editor, tests=yes)	1h 3m 19s
🏁 Windows / Template (target=template_release)	48m 10s
🪲 Godot CPP / Build and test Godot CPP	9m 26s
	9h 8m 23s

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