input: Write a python function to sort a list in descending order.
  assert descending_sort([3, 8, 1, 5]) == [8, 5, 3, 1]
  assert descending_sort([10, 20, 5, 15]) == [20, 15, 10, 5]
  assert descending_sort([4, 2, 9, 6]) == [9, 6, 4, 2]
output: def descending_sort(lst):
      return sorted(lst, reverse=True)