[Live] Use variable - more clear & works if property is null

Author: weaverryan

src/LiveComponent/doc/index.rst

@@ -1477,7 +1477,7 @@ automatically. Let's add the ``save()`` action to the component::
             $this->addFlash('success', 'Post saved!');
 
             return $this->redirectToRoute('app_post_show', [
-                'id' => $this->post->getId(),
+                'id' => $post->getId(),
             ]);
         }
     }