test: fixup worker + source map test

The messaging code uses `Object.defineProperty()`, which accesses
`value` on `Object.prototype` by default, so some calls to the
getter here would actually be expected. Instead, make the list
of accessed properties more specific to the tested source map
code to avoid flakiness.

Refs: https://twitter.com/addaleax/status/1276289101671608320
Refs: https://github.com/nodejs/node/pull/34057

PR-URL: https://github.com/nodejs/node/pull/34446


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>