Astro: XSS via unescaped spread attribute names in renderHTMLElement (incomplete fix for CVE-2026-54298)

Summary The fix for CVE-2026-54298 GHSA-jrpj-wcv7-9fh9 added an INVALIDATTRNAMECHAR guard to addAttribute so that spread-prop attribute names containing "' /= or whitespace are dropped. A second attribute-rendering path, renderHTMLElement in packages/astro/src/runtime/server/render/dom.ts, has it...