docs: Update qa_chat_history tutorial to use non-deprecated method (#9062)

Author: jet-isnt-haha

docs/core_docs/docs/tutorials/qa_chat_history.ipynb

@@ -451,7 +451,7 @@
     "import { BaseMessage, isAIMessage } from \"@langchain/core/messages\";\n",
     "\n",
     "const prettyPrint = (message: BaseMessage) => {\n",
-    "  let txt = `[${message._getType()}]: ${message.content}`;\n",
+    "  let txt = `[${message.getType()}]: ${message.content}`;\n",
     "  if (\n",
     "    (isAIMessage(message) && message.tool_calls?.length) ||\n",
     "    0 > 0\n",