input: Write a python function to find the union of two sets and return it as a list.
  assert union_sets([1, 2, 3], [2, 3, 4, 5]) == [1, 2, 3, 4, 5]
  assert union_sets([5, 6, 7], [7, 8, 9]) == [5, 6, 7, 8, 9]
  assert union_sets([10, 11], [11, 12, 13, 10]) == [10, 11, 12, 13]
output: def union_sets(set1, set2):
      return list(set(set1).union(set(set2)))