style: Don't insert into the seen set before ignoring document colors.

Otherwise we may stop honoring other colors in other cascade levels.

Fixes: #19370

components/style/properties/properties.mako.rs

@@ -3330,7 +3330,6 @@ where
             if seen.contains(physical_longhand_id) {
                 continue
             }
-            seen.insert(physical_longhand_id);
 
             let mut declaration = match *declaration {
                 PropertyDeclaration::WithVariables(id, ref unparsed) => {
@@ -3376,6 +3375,8 @@ where
                 }
             }
 
+            seen.insert(physical_longhand_id);
+
             % if category_to_cascade_now == "early":
                 if LonghandId::FontSize == longhand_id {
                     font_size = Some(declaration.clone());