Web: Clarify that `OS.get_unique_id` is not supported #12117

Job	Run time
📊 Static checks / Code style, file formatting, and docs	55s
🍎 macOS / Editor (target=editor, tests=yes)	42m 59s
🍎 macOS / Template (target=template_release)	33m 29s
🐧 Linux / Editor w/ Mono (target=editor)	5m 57s
🐧 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)	17m 46s
🍏 iOS / Template (target=template_release)	3m 19s
🤖 Android / Template (target=template_release)	4m 27s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	11m 5s
🌐 Web / Template (target=template_release)	1m 51s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	10m 23s
🐧 Linux / Template w/ Mono (target=template_release)	2m 24s
🐧 Linux / Minimal template (target=template_release, everything disabled)	2m 27s
🏁 Windows / Editor (target=editor, tests=yes)	1h 2m 22s
🏁 Windows / Template (target=template_release)	10m 54s
🪲 Godot CPP / Build and test Godot CPP	9m 48s
	3h 40m 6s

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