input: Write a python function to multiply each element in a list by two.
  assert multiply_by_two([1, 2, 3, 4, 5]) == [2, 4, 6, 8, 10]
  assert multiply_by_two([10, 20, 30]) == [20, 40, 60]
  assert multiply_by_two([0, -1, -2]) == [0, -2, -4]
output: def multiply_by_two(lst):
      return [x * 2 for x in lst]