[Frontend] Clarify model_type error messages (vllm-project#9345)

Signed-off-by: Alvant <alvasian@yandex.ru>

Author: stevegrubb

vllm/entrypoints/chat_utils.py

@@ -166,15 +166,15 @@ def _placeholder_str(self, modality: ModalityStr,
             if model_type == "molmo":
                 return ""
 
-            raise TypeError(f"Unknown model type: {model_type}")
+            raise TypeError(f"Unknown {modality} model type: {model_type}")
         elif modality == "audio":
             if model_type == "ultravox":
                 return "<|reserved_special_token_0|>"
-            raise TypeError(f"Unknown model type: {model_type}")
+            raise TypeError(f"Unknown {modality} model type: {model_type}")
         elif modality == "video":
             if model_type == "qwen2_vl":
                 return "<|vision_start|><|video_pad|><|vision_end|>"
-            raise TypeError(f"Unknown model type: {model_type}")
+            raise TypeError(f"Unknown {modality} model type: {model_type}")
         else:
             raise TypeError(f"Unknown modality: {modality}")