[Bug]: Error message returning plain string instead of f-string in image token string retrieval

[luizanao]

Your current environment

Collecting environment information...
PyTorch version: N/A
Is debug build: N/A
CUDA used to build PyTorch: N/A
ROCM used to build PyTorch: N/A

OS: macOS 14.5 (arm64)
GCC version: Could not collect
Clang version: 15.0.0 (clang-1500.3.9.4)
CMake version: version 3.29.6
Libc version: N/A

Python version: 3.10.4 (main, Jun 10 2022, 09:56:45) [Clang 13.1.6 (clang-1316.0.21.2.5)] (64-bit runtime)
Python platform: macOS-14.5-arm64-arm-64bit
Is CUDA available: N/A
CUDA runtime version: Could not collect
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: Could not collect
Nvidia driver version: Could not collect
cuDNN version: Could not collect
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: N/A

CPU:
Apple M1 Max

Versions of relevant libraries:
[pip3] mypy-extensions==0.4.3
[pip3] numpy==1.23.4
[conda] Could not collect
ROCM Version: Could not collect
Neuron SDK Version: N/A
vLLM Version: N/A
vLLM Build Flags:
CUDA Archs: Not Set; ROCm: Disabled; Neuron: Disabled
GPU Topology:
Could not collect

🐛 Describe the bug

When calling a model that does not support images, such:

POST http://vllm:8000/chat/completion/v1
Content-Type: application/json
Accept: application/json

{
    "messages":[
        {
            "role": "user",
            "content": [
                {
                    "type": "text",
                    "text": "...."
                },
                {
                    "type": "image_url",
                    "image_url": {"url": "data:image/jpeg;base64,/9j/......"}
                }
            ]
        }
    ],
    "model": "<ANY-NON-SUPPORTED-MODEL>"
}

the response will be like:

HTTP/1.1 400 Bad Request
date: Wed, 24 Jul 2024 14:08:06 GMT
server: uvicorn
content-length: 112
content-type: application/json
connection: close

{
  "object": "error",
  "message": "Unknown model type: {model_type}",
  "type": "BadRequestError",
  "param": null,
  "code": 400
}

Note that the message is not being interpolated and it is returning a non-expect string.

[DarkLight1337]

Closing as completed by #6748.