test: fix race condition in test-worker-process-cwd.js

This simplifies the test logic and fixes the race condition that
could happen right now.

PR-URL: https://github.com/nodejs/node/pull/28609
Refs: https://github.com/nodejs/node/issues/28193
Closes: https://github.com/nodejs/node/pull/28477
Fixes: https://github.com/nodejs/node/issues/27669
Fixes: https://github.com/nodejs/node/issues/28477


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>