Migrate dropdown_spec to Jest

What does this MR do?

Migrates spec/frontend/ide/components/file_templates/dropdown_spec.js to Jest

Closes #31628 (closed)

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content