Webhook notifier doesn't have secret_settings

nixos/modules/monitoring/server/grafana.nix

@@ -187,7 +187,7 @@ in {
           type = "webhook";
           is_default = true;
           send_reminder = false;
-          secure_settings = {
+          settings = {
             url = "$__file{${toString cfg.grafanaZulipUrlFile}}";
           };
         }]);