Style: Add `WARNING:` as new comment admonition #1593

Job	Run time
📊 Static checks / Code style, file formatting, and docs	34s
🍎 macOS / Editor (target=editor, tests=yes)	28m 42s
🐧 Linux / Editor w/ Mono (target=editor)	36m 39s
🍎 macOS / Template (target=template_release, tests=yes)	26s
🐧 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)	42m 58s
🤖 Android / Editor (target=editor)	22m 56s
🍏 iOS / Template (target=template_release)	8m 29s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	36m 3s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	14m 54s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	14m 38s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	29m 32s
🏁 Windows / Editor (target=editor, tests=yes)	45m 19s
🐧 Linux / Template w/ Mono (target=template_release, tests=yes)	22m 37s
🏁 Windows / Editor w/ clang-cl (target=editor, tests=yes, use_llvm=yes)	38m 23s
🐧 Linux / Minimal template (target=template_release, tests=yes, everything disabled)	13m 48s
🏁 Windows / Template (target=template_release, tests=yes)	31m 59s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	38s
🌐 Web / Template w/o threads (target=template_release, threads=no)	22s
🪲 Godot CPP / Build and test Godot CPP	8m 37s
	6h 37m 34s

Provide feedback