Add more type hints to AdminExtensionInterface

src/Admin/AdminExtensionInterface.php

@@ -99,7 +99,7 @@ public function alterObject(AdminInterface $admin, $object);
     /**
      * Get a chance to add persistent parameters.
      *
-     * @return array
+     * @return array<string, mixed>
      */
     public function getPersistentParameters(AdminInterface $admin);