Use the same ruby version for qa docker image as the rest of the pipeline

What does this MR do and why?

Fetch ruby version from the globally defined when building qa image

Framework code seems to be ruby 3 compatible, no updates required

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR 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 MR.

ruby_3 test run green (selenium failures not related to ruby version): https://gitlab.com/gitlab-org/gitlab/-/pipelines/671021988#/