benchmark: fix worker startup benchmark

It previously called spawnProcess in spawnWorker, which was
incorrect.

PR-URL: #46680
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

benchmark/misc/startup.js

@@ -49,7 +49,7 @@ function spawnWorker(script, bench, state) {
       bench.start();
     }
     if (state.finished < state.count) {
-      spawnProcess(script, bench, state);
+      spawnWorker(script, bench, state);
     } else {
       bench.end(state.count);
     }