Issue #3472203: menu_link_attributes_update_8002 adds container_class attribute if disabled

Closes #3472203

menu_link_attributes.install

@@ -89,11 +89,13 @@ function menu_link_attributes_update_8002(): void {
     ->get('attributes');
 
   // Only set if not yet existing in custom config:
-  if (!isset($attributes['container_class'])) {
-    $attributes['container_class'] = [
-      'label' => 'Container class(es)',
-      'description' => 'CSS class for the menu list item (<li>). Separate multiple classes by space.',
-    ];
+  if (isset($attributes['container_class'])) {
+    if (empty($attributes['container_class']['label'])) {
+      $attributes['container_class']['label'] = 'Container class(es)';
+    }
+    if (empty($attributes['container_class']['description'])) {
+      $attributes['container_class']['description'] = 'CSS class for the menu list item (<li>). Separate multiple classes by space.';
+    }
   }
 
   // Only set if still existing in custom config: