input: Write a function to sort the list items in descending order. The function should directly modify the input list and return None.
  assert sort_descending([3, 7, 5, 8, 10])==None
  assert sort_descending([1, 2, 3, 4, 5])==None
  assert sort_descending([10, 8, 7, 5, 3])==None
  assert sort_descending([])==None
  def sort_descending(lst):
      lst.sort(reverse=True)
output: def sort_descending(lst):
      lst.sort(reverse=True)