input: Write a python function to sort a list of tuples by the second element.
  assert sort_list_tuples([('a', 3), ('b', 2), ('c', 1)]) == [('c', 1), ('b', 2), ('a', 3)]
  assert sort_list_tuples([('x', 5), ('y', 3), ('z', 4)]) == [('y', 3), ('z', 4), ('x', 5)]
  assert sort_list_tuples([('apple', 10), ('banana', 5), ('cherry', 15)]) == [('banana', 5), ('apple', 10), ('cherry', 15)]
output: def sort_list_tuples(lst):
      return sorted(lst, key=lambda x: x[1])