test: fix builds

A former commit changed the tmpDir behavior and that broke the test from #17054 that landed shortly after.

Refs: https://github.com/nodejs/node/commit/bf6ce47259ebfe9f6349c223cc1735726aee062d

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

test