test: improve test-gc-http-client-connaborted

* refactor out usage of 'function' for scoping
* wait till server is up to start firing requests

PR-URL: https://github.com/nodejs/node/pull/23193


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>