test: fix missing cb in fs.unlink

[legendecas]

Fix CI failure in nodejs/gyp-next#357.

  1) addon
       build simple addon in path with non-ascii characters:
     TypeError [ERR_INVALID_ARG_TYPE]: The "cb" argument must be of type function. Received undefined
      at makeCallback (node:fs:186:3)
      at Object.unlink (node:fs:1989:14)
      at Context.<anonymous> (test\test-addon.js:114:10)
      at process.processTicksAndRejections (node:internal/process/task_queues:104:5)

Checklist

• npm install && npm run lint && npm test passes
• tests are included