input: Write a python function to find common elements between two lists.
  assert common_elements([1, 2, 3, 4], [2, 4, 6]) == [2, 4]
  assert common_elements([10, 20, 30], [15, 25, 30]) == [30]
  assert common_elements([5, 7, 9], [7, 8, 10]) == [7]
output: def common_elements(list1, list2):
      return list(set(list1) & set(list2))