Use new Ruby 2.7.7 linting image

What does this MR do and why?

Use latest Ruby 2.7.7-based linting image to match the version of Ruby we already use in the project.

Merge request acceptance checklist

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

• I have evaluated the MR acceptance checklist for this merge request.