input: Write a python function to swap keys and values of a dictionary where values become keys and keys become values stored in a list.
  assert swap_dict_keys_values({'a': 1, 'b': 2, 'c': 1}) == {1: ['a', 'c'], 2: ['b']}
  assert swap_dict_keys_values({1: 'x', 2: 'y', 3: 'x'}) == {'x': [1, 3], 'y': [2]}
  assert swap_dict_keys_values({'apple': 'fruit', 'carrot': 'vegetable', 'banana': 'fruit'}) == {'fruit': ['apple', 'banana'], 'vegetable': ['carrot']}
output: def swap_dict_keys_values(d):
      new_dict = {}
      for key, value in d.items():
          if value not in new_dict:
              new_dict[value] = []
          new_dict[value].append(key)
      return new_dict