fix: ensure Listener connections are released

retryingListen function potentially leaks database connections. This patch ensures the connections are released in case of listen/notify errors.

src/PostgREST/Observation.hs

@@ -50,6 +50,7 @@ data Observation
   | DBListenBugHint -- https://github.com/PostgREST/postgrest/issues/3147
   | DBListenerGotSCacheMsg ByteString
   | DBListenerGotConfigMsg ByteString
+  | DBListenerConnectionCleanupFail SomeException
   | QueryObs MainQuery Status
   | ConfigReadErrorObs SQL.UsageError
   | ConfigInvalidObs Text
@@ -122,6 +123,8 @@ observationMessage = \case
     "Received a schema cache reload message on the " <> show channel <> " channel"
   DBListenerGotConfigMsg channel ->
     "Received a config reload message on the " <> show channel <> " channel"
+  DBListenerConnectionCleanupFail ex ->
+    "Failed during listener connection cleanup: " <> showOnSingleLine '\t' (show ex)
   QueryObs{} ->
     mempty -- TODO pending refactor: The logic for printing the query cannot be done here. Join the observationMessage function into observationLogger to avoid this mempty.
   ConfigReadErrorObs usageErr ->