Fix track-level genre handling in lastgenre plugin

When `lastgenre.source: track` is configured,

- `lastgenre -a` _should not_ fall back to the album level genre (by
  making use of the with_album=False kwarg of the Libary's get method).
- `lastgenre -a`, when finally storing the genres of _an album_, should
  _not_ also write the tracks genres (by making use of the inherit=False
  kwarg of the Album's store method.

beetsplug/lastgenre/__init__.py

@@ -411,7 +411,7 @@ class LastGenrePlugin(plugins.BeetsPlugin):
                     self._log.info(
                         "genre for album {0} ({1}): {0.genre}", album, src
                     )
-                    album.store()
+                    album.store(inherit=False)
 
                     for item in album.items():
                         # If we're using track-level sources, also look up each