chore: Update backend.py

Author: bradhilton

src/art/serverless/backend.py

@@ -78,8 +78,9 @@ async def _delete_checkpoints(
             if metric is not None and (max_metric is None or metric > max_metric):
                 max_metric = metric
                 max_step = checkpoint.step
+            print(f"Checkpoint: {checkpoint.step} {metric}")
             all_steps.append(checkpoint.step)
-        steps_to_delete = [step for step in all_steps[:-1] if step != max_step]
+        steps_to_delete = [step for step in all_steps[1:] if step != max_step]
         if steps_to_delete:
             await self._client.checkpoints.delete(
                 model_id=model.id,