message: Handle the case where axis is a tuple.
  Previously the code only handled ints and lists as axis. Gave an error `TypeError: 'tuple' object does not support item assignment` when giving tuple as axis argument. See this issue
diff: @@ -954,6 +954,8 @@ class LayerNormalization(Layer):
  # Convert axis to list and resolve negatives
  if isinstance(self.axis, int):
  self.axis = [self.axis]
  + elif isinstance(self.axis, tuple):
  + self.axis = list(self.axis)
  for idx, x in enumerate(self.axis):
  if x < 0:
  self.axis[idx] = ndims + x
  