Fix passing of keyword args to Dense layers in create_tower

[b4russell]

Current behavior: kwargs are passed to tf.keras.Sequential.add, so they are not passed on to tf.keras.layers.Dense as intended. For example, when passing use_bias=False to create_tower with the kwarg name kernel_regularizer, it throws an exception:

Traceback (most recent call last):
  File "/Users/brussell/development/ranking/tensorflow_ranking/python/keras/layers_test.py", line 33, in test_create_tower_with_kwargs
    tower = layers.create_tower([3, 2, 1], 1, activation='relu', use_bias=False)
  File "/Users/brussell/development/ranking/tensorflow_ranking/python/keras/layers.py", line 70, in create_tower
    model.add(tf.keras.layers.Dense(units=layer_width), **kwargs)
  File "/usr/local/anaconda3/lib/python3.9/site-packages/tensorflow/python/trackable/base.py", line 205, in _method_wrapper
    result = method(self, *args, **kwargs)
  File "/usr/local/anaconda3/lib/python3.9/site-packages/keras/utils/traceback_utils.py", line 61, in error_handler
    return fn(*args, **kwargs)
TypeError: add() got an unexpected keyword argument 'use_bias' test_create_tower_with_kwargs

Fix: This PR fixes the behavior by shifting the closing paren of tf.keras.layers.Dense to the correct location.

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[b4russell]

Hi! I want to follow up on this PR, which has been open for a year. Are you interested in fixing this behavior or should I close the PR? Tagging @lyyanlely , since you incorporated my colleague @JackGammack PR recently.