Update pgembedding.ipynb (#7699)

Update the extension name. It changed from pg_hnsw to pg_embedding.

Thank you. I missed this in my previous commit.

docs/extras/modules/data_connection/vectorstores/integrations/pgembedding.ipynb

@@ -6,7 +6,7 @@
    "id": "1292f057",
    "metadata": {},
    "source": [
-    "# pg_hnsw\n",
+    "# pg_embedding\n",
     "\n",
     "> [pg_embedding](https://github.com/neondatabase/pg_embedding) is an open-source vector similarity search for `Postgres` that uses  Hierarchical Navigable Small Worlds for approximate nearest neighbor search.\n",
     "\n",