listenbrainz-mpd: use sdnotify when possible

The ability for listenbrainz-mpd to notify systemd when it's ready was
added in 2.3.2:

https://codeberg.org/elomatreb/listenbrainz-mpd/releases/tag/v2.3.2

modules/services/listenbrainz-mpd.nix

@@ -40,6 +40,10 @@ in {
         ExecStart = "${cfg.package}/bin/listenbrainz-mpd";
         Restart = "always";
         RestartSec = 5;
+        Type = if lib.versionAtLeast cfg.package.version "2.3.2" then
+          "notify"
+        else
+          "simple";
       };
       Install.WantedBy = [ "default.target" ];
     };