Clarify `_search_spotify` return type
Clarify `_search_spotify` return type

shamangeorge/beets,jackwilsdon/beets,beetbox/beets,sampsyo/beets,shamangeorge/beets,jackwilsdon/beets,sampsyo/beets,jackwilsdon/beets,shamangeorge/beets,sampsyo/beets,ibmibmibm/beets,SusannaMaria/beets,ibmibmibm/beets,SusannaMaria/beets,sampsyo/beets,ibmibmibm/beets,SusannaMaria/beets,beetbox/beets,shamangeorge/beets,jackwilsdon/beets,SusannaMaria/beets,beetbox/beets,beetbox/beets,ibmibmibm/beets