Fix ruff formatting (#438)

Author: arcticfly

src/art/local/backend.py

@@ -488,9 +488,9 @@ async def _train_model(
             num_gradient_steps = int(
                 result.pop("num_gradient_steps", estimated_gradient_steps)
             )
-            assert (
-                num_gradient_steps == estimated_gradient_steps
-            ), f"num_gradient_steps {num_gradient_steps} != estimated_gradient_steps {estimated_gradient_steps}"
+            assert num_gradient_steps == estimated_gradient_steps, (
+                f"num_gradient_steps {num_gradient_steps} != estimated_gradient_steps {estimated_gradient_steps}"
+            )
             results.append(result)
             yield {**result, "num_gradient_steps": num_gradient_steps}
             pbar.update(1)