input: Write a python function to iterate over a dictionary and print its keys and values in the format "key : value".
  assert print_dict_items({'a': 1, 'b': 2, 'c': 3}) == "a : 1\nb : 2\nc : 3\n"
  assert print_dict_items({'name': 'Alice', 'age': 30, 'city': 'Wonderland'}) == "name : Alice\nage : 30\ncity : Wonderland\n"
  assert print_dict_items({}) == ""
output: def print_dict_items(d):
      result = ''
      for key, value in d.items():
          result += f"{key} : {value}\n"
      return result