test: add test-worker-prof to the SLOW list for debug

Consistently failing on ubuntu1804_sharedlibs_debug_x64

Refs: https://github.com/nodejs/node/issues/26401

PR-URL: https://github.com/nodejs/node/pull/32589


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>