test: more robust check for location of `node.exe`

look for the actual produced `exe` not just the directory

PR-URL: https://github.com/nodejs/node/pull/12120


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Nikolai Vavilov <vvnicholas@gmail.com>