input: Write a python function to print dictionary keys and values.
  assert print_dict({'name': 'Alice', 'age': 30}) == None
  assert print_dict({'x': 10, 'y': 20, 'z': 30}) == None
  assert print_dict({}) == None
output: def print_dict(d):
      for key, value in d.items():
          print(f"{key}: {value}")