input: Write a python function to sort a list in descending order using a lambda function.
  assert sort_list_desc([1, 5, -9, 8, 21]) == [21, 8, 5, 1, -9]
  assert sort_list_desc([10, 3, 45, 67, 84, 93]) == [93, 84, 67, 45, 10, 3]
  assert sort_list_desc([5, 7, 9, 8, 6, 4, 3]) == [9, 8, 7, 6, 5, 4, 3]
output: def sort_list_desc(lst):
      return sorted(lst, key=lambda x: -x)