input: Write a python function to return the unique elements from a list.
  assert unique_elements([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert unique_elements([10, 20, 20, 30, 40, 40, 50]) == [10, 20, 30, 40, 50]
  assert unique_elements([5, 5, 5, 5, 5, 5]) == [5]
output: def unique_elements(lst):
      return list(set(lst))