test: fix tests so they work in worker threads

Use the `cwd` option for child_process instead of `process.chdir()` to
allow tests to work with worker threads.

PR-URL: https://github.com/nodejs/node/pull/26453


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>