Tests the signed exchange information are available when the prefetch succeeded.

* http://127.0.0.1:8000/loading/sxg/resources/sxg-location.sxg
  failed: false
  statusCode: 200
  resourceType: signed-exchange
  SignedExchangeInfo
    Request URL: https://127.0.0.1:8443/loading/sxg/resources/inner-url.html
    Certificate URL: https://127.0.0.1:8443/loading/sxg/resources/127.0.0.1.sxg.pem.cbor
    Certificate Subject: 127.0.0.1
    Certificate Issuer: web-platform-tests
* https://127.0.0.1:8443/loading/sxg/resources/127.0.0.1.sxg.pem.cbor
  failed: false
  statusCode: 200
  resourceType: other
* https://127.0.0.1:8443/loading/sxg/resources/inner-url.html
  failed: false
  statusCode: 200
  resourceType: other