input: Write a python function to convert a string to a list of ASCII values.
  assert string_to_ascii_list("Hello") == [72, 101, 108, 108, 111]
  assert string_to_ascii_list("World!") == [87, 111, 114, 108, 100, 33]
  assert string_to_ascii_list("Python3.9") == [80, 121, 116, 104, 111, 110, 51, 46, 57]
output: def string_to_ascii_list(s):
      return [ord(char) for char in s]