Mutation input: typo on 'add_items_playlist_input.py' missing '_to'

[phdye]

On the line prefixed by ‘!’, the file name ‘add_items_playlist_input.py’ should be ‘add_items_to_playlist_input.py’.

### The `AddItemsToPlaylistInput` type

! Let’s create a new file called add_items_playlist_input.py under the api/types
folder and define a class called AddItemsToPlaylistInput .