test: improve test-gc-http-client

Calling `global.gc()` in multiple places leads to unreliability. Call it
in the interval only.

PR-URL: #23145
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

test/sequential/test-gc-http-client.js

@@ -43,7 +43,6 @@ function getall() {
 function cb(res) {
   res.resume();
   done += 1;
-  res.on('end', global.gc);
 }
 
 function ongc() {