LibWeb: Make factory method of CSS::CSSStyleRule fallible

Author: https://github.com/kennethmyhra
Commit: 4f4a908e5f
Pull-request: https://github.com/SerenityOS/serenity/pull/17491
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -3120,7 +3120,7 @@ CSSRule* Parser::convert_to_rule(NonnullRefPtr<Rule> rule)
         return {};
     }
 
-    return CSSStyleRule::create(m_context.realm(), move(selectors.value()), *declaration);
+    return CSSStyleRule::create(m_context.realm(), move(selectors.value()), *declaration).release_value_but_fixme_should_propagate_errors();
 }
 
 auto Parser::extract_properties(Vector<DeclarationOrAtRule> const& declarations_and_at_rules) -> PropertiesAndCustomProperties