input: Write a python function to modify the list by adding a given value to each element.
  assert modify_list([10, 11, 12, 13, 14], 1) == [11, 12, 13, 14, 15]
  assert modify_list([1, 2, 3, 4, 5], 5) == [6, 7, 8, 9, 10]
  assert modify_list([0, 0, 0, 0], 10) == [10, 10, 10, 10]
output: def modify_list(lst, val):
      return [x + val for x in lst]