fix service worker security issue

What does this MR do and why?

Fix a security issue raised by sonar

How to set up and validate locally

There no way to check it because the code that raised the issue never got run anyway.

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?