test: fix test-heapdump-worker

This test was broken by de2c68c7.

Refs: https://github.com/nodejs/node/pull/31386

PR-URL: https://github.com/nodejs/node/pull/31494


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>