Fix HTML attribute name normalization (#19709)

src/language-html/parse/postprocess.js

@@ -241,9 +241,9 @@ function normalizeName(node, parseOptions) {
           attr.name = lowerCaseIf(
             attr.name,
             (lowerCasedAttrName) =>
-              ELEMENT_ATTRIBUTES.has(node.name) &&
+              HTML_TAGS.has(node.name) &&
               (GLOBAL_ATTRIBUTES.has(lowerCasedAttrName) ||
-                ELEMENT_ATTRIBUTES.get(node.name).has(lowerCasedAttrName)),
+                ELEMENT_ATTRIBUTES.get(node.name)?.has(lowerCasedAttrName)),
           );
         }
       }