Cancel PGListener reader async when a subscription is stopped

This avoids asyncs building up over time

IHP/PGListener.hs

@@ -164,6 +164,7 @@ unsubscribe subscription@(Subscription { .. }) pgListener = do
         deleteById :: [Subscription] -> [Subscription]
         deleteById = List.deleteBy (\a b -> get #id a == get #id b) subscription
     modifyIORef' (get #subscriptions pgListener) (HashMap.adjust deleteById channel)
+    uninterruptibleCancel reader
     pure ()     
 
 -- | Runs a @LISTEN ..;@ statements on the postgres connection, if not already listening on that channel