message: fix duplicated assignment to response header in log
diff: @@ -1629,7 +1629,7 @@ void Context::log(const Http::HeaderMap* request_headers, const Http::HeaderMap*
  access_log_request_headers_ = request_headers;
  // ? request_trailers ?
  access_log_response_headers_ = response_headers;
  - access_log_response_headers_ = response_trailers;
  + access_log_response_trailers_ = response_trailers;
  access_log_stream_info_ = &stream_info;
  onLog();
  @@ -1637,7 +1637,7 @@ void Context::log(const Http::HeaderMap* request_headers, const Http::HeaderMap*
  access_log_request_headers_ = nullptr;
  // ? request_trailers ?
  access_log_response_headers_ = nullptr;
  - access_log_response_headers_ = nullptr;
  + access_log_response_trailers_ = nullptr;
  access_log_stream_info_ = nullptr;
  onDelete();
  