input: Write a python function to multiply each element in a list by a given integer.
  assert multiply_by_int([1, 2, 3, 4], 2) == [2, 4, 6, 8]
  assert multiply_by_int([5, 10, 15], 3) == [15, 30, 45]
  assert multiply_by_int([0, -1, -2], -3) == [0, 3, 6]
output: def multiply_by_int(lst, n):
      return [x * n for x in lst]