Ensure unique config names

Closes #3485370

src/ReadOnlyFormEvent.php

@@ -105,7 +105,7 @@ class ReadOnlyFormEvent extends Event {
    *   The config names to be set in the event.
    */
   public function setEditableConfigNames(array $config_names): void {
-    $this->configNames = $config_names;
+    $this->configNames = array_unique($config_names);
   }
 
   /**