nextcloud-notify_push.tests: fix eval

Without the change the eval fails as:

    $ nix build --no-link -f. nextcloud-notify_push.tests
    error: attribute 'with-postgresql-and-redis26' missing
           at pkgs/servers/nextcloud/notify_push.nix:35:9:
               34|       inherit (nixosTests.nextcloud)
               35|         with-postgresql-and-redis26
                 |         ^
               36|         with-postgresql-and-redis27
           Did you mean one of with-postgresql-and-redis27, with-postgresql-and-redis28 or with-postgresql-and-redis29?

pkgs/servers/nextcloud/notify_push.nix

@@ -32,9 +32,9 @@ rustPlatform.buildRustPackage rec {
     };
     tests = {
       inherit (nixosTests.nextcloud)
-        with-postgresql-and-redis26
         with-postgresql-and-redis27
-        with-postgresql-and-redis28;
+        with-postgresql-and-redis28
+        with-postgresql-and-redis29;
       inherit test_client;
     };
   };