fix(sharded): properly unsubscribe when closing

Providing an array of channels to the SUNSUBSCRIBE command assumes all
the channels are allocated to the same slot, which is not always the
case, so we need to issue one command per channel.

Related: #500

lib/sharded-adapter.ts

@@ -108,7 +108,9 @@ class ShardedRedisAdapter extends ClusterAdapter {
       });
     }
 
-    return SUNSUBSCRIBE(this.subClient, channels);
+    return Promise.all(
+      channels.map((channel) => SUNSUBSCRIBE(this.subClient, channel))
+    ).then();
   }
 
   override publishMessage(message) {