🐛 Bug: .eslint-doc-generatorrc.js should be .mjs in CJS packages

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Expected

The blockESLintPlugin config file's type should be a .mjs when the package.json specifies "type": "commonjs".

Actual

JoshuaKGoldberg/eslint-plugin-package-json#993 (comment): it's still .js.

Additional Info

🎁

[JoshuaKGoldberg]

Fixed by #2138.