Fix wrong shape used for concrete function

PiperOrigin-RevId: 504395908

Author: faizan-m

site/en/guide/saved_model.ipynb

@@ -682,7 +682,7 @@
         "    super(CustomModuleWithOutputName, self).__init__()\n",
         "    self.v = tf.Variable(1.)\n",
         "\n",
-        "  @tf.function(input_signature=[tf.TensorSpec([], tf.float32)])\n",
+        "  @tf.function(input_signature=[tf.TensorSpec(None, tf.float32)])\n",
         "  def __call__(self, x):\n",
         "    return {'custom_output_name': x * self.v}\n",
         "\n",