input: Write a python function to combine two lists.
  assert combine_list([1, 2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]
  assert combine_list(['a', 'b'], ['c', 'd', 'e']) == ['a', 'b', 'c', 'd', 'e']
  assert combine_list([], [1, 2, 3]) == [1, 2, 3]
output: def combine_list(list1, list2):
      return list1 + list2