input: Write a function to print a dictionary where each key-value pair is displayed in the format "key: value".
  assert print_dict({"a": 1, "b": 2, "c": 3}) is None
  assert print_dict({"x": 10, "y": 20}) is None
  assert print_dict({}) is None
output: def print_dict(d):
      for key, value in d.items():
          print(f"{key}: {value}")