input: Write a python function to combine two lists into a list of tuples.
  assert combine_lists([1, 2, 3, 4], [5, 6, 7, 8])==[(1, 5), (2, 6), (3, 7), (4, 8)]
  assert combine_lists([10, 20], [30, 40])==[(10, 30), (20, 40)]
  assert combine_lists([1, 3, 5], [2, 4, 6])==[(1, 2), (3, 4), (5, 6)]
output: def combine_lists(list1, list2):
      return list(zip(list1, list2))