file add_albums.py / Use album.artists.set(artists) instead of album.artists = artists

[oussema-azzebi]

Error in line 46 (before the last one) :
album.artists = artists

• The error message in the python console :
  Direct assignment to the forward side of a many-to-many set is prohibited. Use artists.set()
  instead.

• Replace with:
  album.artists.set(artists)