Fix failure in windowed_sampling_test.jax in OSS.

PiperOrigin-RevId: 453202511

Author: jburnim

tensorflow_probability/python/experimental/mcmc/windowed_sampling.py

@@ -269,8 +269,9 @@ def step_broadcast(step_size):
   shard_axis_names = pinned_model.experimental_shard_axis_names
   if any(tf.nest.flatten(shard_axis_names)):
     shard_axis_names = nest.flatten_up_to(
-        initial_transformed_position, pinned_model._model_flatten(  # pylint: disable=protected-access
-            shard_axis_names))
+        initial_transformed_position,
+        list(pinned_model._model_flatten(shard_axis_names)))  # pylint: disable=protected-access
+
   else:
     # No active shard axis names
     shard_axis_names = None