fix: pin ESLint to v8

[AlCalzone]

PR Checklist:

• Provide a meaningful description to this PR or mention which issues this fixes.
• Ensure the project builds with npm run build
• Add tests for your change. This includes negative tests (i.e. inputs that need to fail) as well as baseline tests (i.e. how should the directory structure look like?).
• Run the test suite with npm test
• If there are baseline changes, review them and make a separate commit for them with the comment "accept baselines" if they are desired changes
• If you added a required option, also add it to the template creation (.github/create_templates.ts)
• Add a detailed migration description to docs/updates explaining what the user needs to do when manually updating an existing project
• Add your changes to CHANGELOG.md (referencing the migration description and this PR or the issue you fixed)

Description:
This is needed for now until typescript-eslint supports ESLint v9. When that is done, we can migrate to the new config format and update everything ESLint-related.