Update google_vertex_ai_palm.ipynb (#12715)

Fixed a typo

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docs/docs/integrations/llms/google_vertex_ai_palm.ipynb

@@ -404,7 +404,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "chian = prompt | llm\n",
+    "chain = prompt | llm\n",
     "print(chain.invoke({\"thing\": \"life\"}))"
    ]
   }