这个错误是因为客户端在尝试访问服务器时使用了HTTP协议，而服务器需要使用HTTPS协议。要解决这个问题，你需要将客户端代码中的URL从openai_api_base更改为openai_api_base.replace("http://", "https://")。

修改后的代码如下：

from openai import OpenAI

# Set OpenAI's API key and API base to use vLLM's API server.

openai_api_key = "vllm-abc123456"
openai_api_base = "[http://192.168.2.6:8000/v1](http://192.168.2.6:8000/v1)"
client = OpenAI(
    api_key=openai_api_key,
    base_url=openai_api_base.replace("http://", "https://"),
)
chat_response = client.chat.completions.create(
    model="nvidia/Llama3-ChatQA-1.5-8B",
    messages=[
        {"role": "system", "content": "You are a helpful assistant."},
        {"role": "user", "content": "Tell me a joke."},
    ],
    extra_body={
        "guided_choice": ["positive", "negative"]
    }
).choices[0].message.content
print("Chat response:", chat_response)