Fixed a ValidationError when requesting a Playlist without a cover image

[Kuwertzel]

Changed the type the of the images attribute in the Playlist base class to a nullable list to avoid a pydantic ValidationError in cases where the API returns null. This happens when requesting an empty playlist without a custom image.

Related issue: none created

• Tests written with 100% coverage
• Documentation and changelog entry written

Some tox checks have failed in my environment, though the errors don't seem to be related to the implemented change.

I have manually tested the change by requesting an emtpy playlist using spotify.playlist('<playlist-id>'), which resulted in the following (shortened) traceback prior to the change:

pydantic_core._pydantic_core.ValidationError: 1 validation error for FullPlaylist
images
  Input should be a valid list [type=list_type, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.3/v/list_type

[felix-hilden]

Thank you for submitting the fix directly! Just a wording update suggestion on the changelog, I like to keep a certain style and add links 👌