input: Write a python function to print key-value pairs in a dictionary.
  assert print_key_value_pairs({"a": 1, "b": 2, "c": 3}) == "a: 1\nb: 2\nc: 3\n"
  assert print_key_value_pairs({"x": 10, "y": 20}) == "x: 10\ny: 20\n"
  assert print_key_value_pairs({}) == ""
output: def print_key_value_pairs(d):
      result = ""
      for key, value in d.items():
          result += f"{key}: {value}\n"
      return result