mpris: fix artist name

https://www.freedesktop.org/wiki/Specifications/mpris-spec/metadata says artist is a list

Fixes the issue for me in Gnome

sublime_music/dbus/manager.py

@@ -339,7 +339,7 @@ class DBusManager:
             # TODO (#71) use walrus once MYPY isn't retarded
             "xesam:album": (song.album.name if song.album else ""),
             "xesam:albumArtist": [artist_name],
-            "xesam:artist": artist_name,
+            "xesam:artist": [artist_name],
             "xesam:title": song.title,
         }