[Frontend] Fix logging format when enable response logging (vllm-project#28049)

Signed-off-by: esmeetu <[email protected]>

Author: esmeetu

vllm/entrypoints/openai/api_server.py

@@ -1572,8 +1572,7 @@ def buffered_iterator():
                             full_content = full_content[:2048] + ""
                             "...[truncated]"
                         logger.info(
-                            "response_body={streaming_complete: "
-                            "content='%s', chunks=%d}",
+                            "response_body={streaming_complete: content=%r, chunks=%d}",
                             full_content,
                             chunk_count,
                         )