bug: /headers x-request-id not passed to response body

[gtors]

~ >>> curl -i http://httpbin.org/headers -H 'x-request-id: avadakedavra'
HTTP/1.1 200 OK
Date: Thu, 25 Feb 2021 08:52:35 GMT
Content-Type: application/json
Content-Length: 173
Connection: keep-alive
Server: gunicorn/19.9.0
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true

{
  "headers": {
    "Accept": "*/*",
    "Host": "httpbin.org",
    "User-Agent": "curl/7.75.0",
    "X-Amzn-Trace-Id": "Root=1-60376553-2b9d0703199a24c10c2b30f2"
  }
}

[lucasantarella]

I also see this.