message: In optimizer_v2, adds a comment saying the check for `callable` covers the usage when `value` is a `LearningRateSchedule`.
diff: @@ -813,6 +813,9 @@ class OptimizerV2(trackable.Trackable):
  for name, value in sorted(self._hyper.items()):
  if isinstance(value,
  (ops.Tensor, tf_variables.Variable)) or callable(value):
  + # The check for `callable` covers the usage when `value` is a
  + # `LearningRateSchedule`, in which case it does not need to create a
  + # variable.
  continue
  else:
  self._hyper[name] = self.add_weight(
  