[tune] Only try to sync driver if sync_to_driver is actually enabled (#…

…19589)

python/ray/tune/syncer.py

@@ -418,7 +418,10 @@ def _sync_trial_checkpoint(self, trial: "Trial", checkpoint: Checkpoint):
         from ray.tune.durable_trainable import DurableTrainable
 
         trial_syncer = self._get_trial_syncer(trial)
-        if trial.sync_on_checkpoint:
+        # If the sync_function is False, syncing to driver is disabled.
+        # In every other case (valid values include None, True Callable,
+        # NodeSyncer) syncing to driver is enabled.
+        if trial.sync_on_checkpoint and self._sync_function is not False:
             try:
                 # Wait for any other syncs to finish. We need to sync again
                 # after this to handle checkpoints taken mid-sync.