compare url attribute names case-insensitively when sanitizing

[NullVoxPopuli]

checkURI and checkDataURI matched attribute names against the lowercase badAttributes lists with a strict comparison, so a mixed-case name such as HREF or SRC bypassed the javascript:/vbscript: protocol check even though requiresSanitization still routed the element through the sanitizer.

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Supersedes: #21430

Repro: https://limber.glimdown.com/edit?c=MYewdgzgLgBAZiEMC8MDkArAhgNyxYAJwEsAHKALlEhABsBTAOlpAHMAKAIgAtjOBKNAG4AUCIA8UegFtStLFIB8ImDHFYY3QvTjIA3noQgAvscVad4gPRZlq9TAASAJQCiAMX2HEpxS4-WthJWUrLySkA&format=gjs

[github-actions]

📊 Size report

Tarball size — 1.2 MB → 1.2 MB

dist/dev   0%↑

File	Before (Size / Brotli)	After (Size / Brotli)
Total (Includes all files)	2 MB / 479.3 kB	0%↑2 MB / 0.01%↑479.4 kB

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dist/prod   0%↑

File	Before (Size / Brotli)	After (Size / Brotli)
./packages/shared-chunks/api-{hash}.js	5.9 kB / 1.5 kB	40%↑8.3 kB / 21%↑1.8 kB
Total (Includes all files)	1.8 MB / 437.2 kB	0%↑1.8 MB / -0%↓437.2 kB

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smoke-tests/v2-app-hello-world-template/dist   0.01%↑

File	Before (Size / Brotli)	After (Size / Brotli)
Total (Includes all files)	235 kB / 64.4 kB	0.01%↑235 kB / 0.1%↑64.4 kB

_{🤖 This report was automatically generated by wyvox/pkg-size}