Fix logic in bedrock server import frontend

What does this MR do and why?

Fix JS variable definition that was causing bedrock wizard root files buttons to not respond to user click events.

Resolves #486 (closed)

How to set up and validate locally

1. upload a zipfile for server import
2. Click the root files button

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• Have you checked this doesn't interfere/conflict/duplicate someone elses work?
• Have you fully tested your changes?
• Have you resolved any lint issues?
• Have you assigned a reviewer?
• Have you applied correct labels?