ollama: only set `updateScript` for `ollama`, not `ollama-{rocm,cuda}` (#345375)

pkgs/by-name/ol/ollama/package.nix

···
         service-cuda = nixosTests.ollama-cuda;
         service-rocm = nixosTests.ollama-rocm;
       };
-
-    updateScript = nix-update-script { };
-  };
+  } // lib.optionalAttrs (!enableRocm && !enableCuda) { updateScript = nix-update-script { }; };
 
   meta = {
     description =