input: Write a python function to split a comma-separated string into a list of integers.
  assert split_string_to_int_list("1,2,3,4,5") == [1, 2, 3, 4, 5]
  assert split_string_to_int_list("10,20,30,40,50") == [10, 20, 30, 40, 50]
  assert split_string_to_int_list("7,8,9") == [7, 8, 9]
output: def split_string_to_int_list(s):
      return [int(x) for x in s.split(',')]