Update graph_constructing.ipynb (#28489)

Used llm_transformer_tuple instance to create graph documents and
assigned to graph_documents_filtered variable.

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docs/docs/how_to/graph_constructing.ipynb

@@ -245,7 +245,7 @@
     "    allowed_nodes=[\"Person\", \"Country\", \"Organization\"],\n",
     "    allowed_relationships=allowed_relationships,\n",
     ")\n",
-    "llm_transformer_tuple = llm_transformer_filtered.convert_to_graph_documents(documents)\n",
+    "graph_documents_filtered = llm_transformer_tuple.convert_to_graph_documents(documents)\n",
     "print(f\"Nodes:{graph_documents_filtered[0].nodes}\")\n",
     "print(f\"Relationships:{graph_documents_filtered[0].relationships}\")"
    ]