message: Remove the usage of ds combination.concat, and replace it with raw list concat.
diff: @@ -38,14 +38,13 @@ class OptimizerTest(test.TestCase, parameterized.TestCase):
  distribution=strategy_combinations.multidevice_strategies,
  mode=["eager"],
  ),
  - ds_combinations.concat(
  combinations.combine(
  experimental_aggregate_gradients=True,
  - expected=[[[-0.3, -0.3], [-0.3, -0.3]]]),
  + expected=[[[-0.3, -0.3], [-0.3, -0.3]]]) +
  combinations.combine(
  experimental_aggregate_gradients=False,
  - expected=[[[-0.1, -0.1], [-0.2, -0.2]]]),
  - )))
  + expected=[[[-0.1, -0.1], [-0.2, -0.2]]])
  + ))
  def test_custom_aggregation(self, distribution,
  experimental_aggregate_gradients, expected):
  