🛠️ Repo: Convert `lib/nodejs/file-unloader.js` to ESM

[JoshuaKGoldberg]

Tooling Suggestion Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Splitting out of #5968: lib/nodejs/file-unloader.js has a require cache setting that makes it not _directly– switchable to ESM immediately.

mocha/lib/nodejs/file-unloader.js

Line 14 in 6695fba

delete require.cache[require.resolve(file)];

Additional Info

No response