Fix incorrect logic related to --keep_last_checkpoint_only

We should not assign a value to this parameter, as it takes no values.

Signed-off-by: Courtney Pacheco <6019922+courtneypacheco@users.noreply.github.com>

Author: courtneypacheco

src/instructlab/training/main_ds.py

@@ -707,9 +707,11 @@ def run_training(torch_args: TorchrunArgs, train_args: TrainingArgs) -> None:
         f"--max_batch_len={train_args.max_batch_len}",
         f"--seed={train_args.random_seed}",
         f"--chat-tmpl-path={train_args.chat_tmpl_path}",
-        f"--keep_last_checkpoint_only={train_args.keep_last_checkpoint_only}",
     ]
 
+    if train_args.keep_last_checkpoint_only:
+        command.append(f"--keep_last_checkpoint_only")
+
     if train_args.checkpoint_at_epoch:
         command.append("--checkpoint_at_epoch")