LibWeb: Make Serialize functions infallible

Author: https://github.com/AtkinsSJ
Commit: b5893ee115
Pull-request: https://github.com/SerenityOS/serenity/pull/20709

Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.cpp

@@ -41,13 +41,13 @@ DeprecatedString CSSNamespaceRule::serialized() const
 
     // followed by the serialization as an identifier of the prefix attribute (if any),
     if (!m_prefix.is_empty() && !m_prefix.is_null()) {
-        serialize_an_identifier(builder, m_prefix).release_value_but_fixme_should_propagate_errors();
+        serialize_an_identifier(builder, m_prefix);
         // followed by a single SPACE (U+0020) if there is a prefix,
         builder.append(" "sv);
     }
 
     //  followed by the serialization as URL of the namespaceURI attribute,
-    serialize_a_url(builder, m_namespace_uri).release_value_but_fixme_should_propagate_errors();
+    serialize_a_url(builder, m_namespace_uri);
 
     // followed the character ";" (U+003B).
     builder.append(";"sv);