fix: Update method call to use correct object instance

Author: CodeWithDennis

src/SelectTree.php

@@ -134,7 +134,7 @@ protected function setUp(): void
 
             $form->model($record)->saveRelationships();
 
-            return $this->getCustomKey($record);
+            return $component->getCustomKey($record);
         });
 
         $this->suffixActions([