test: refactored test-http-allow-req-after-204-res to countdown

PR-URL: https://github.com/nodejs/node/pull/17211


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>