Fix typos in 'run_on_backend'

Author: kephircheek

notebooks/hd_tomography.ipynb

@@ -36917,7 +36917,7 @@
     "    if not assets_path.exists():\n",
     "        assets_path.mkdir()\n",
     "    if not assets_path.is_dir():\n",
-    "        raise TypeError(\"is not a directory: {assets_path}\")\n",
+    "        raise TypeError(f\"is not a directory: {assets_path}\")\n",
     "\n",
     "    result_path_base = rf\"result-{circuit.name}-{backend.name}-{shots}\"\n",
     "    maps_str = maps2str(maps) if maps is not None else None\n",