ci: group ruby-version updates together

Andrew Newdigaterequested to merge
group-ruby-version-updates into main

On some repositories, like Runbooks, the ruby-version number is duplicated in .tool-versions and .ruby-version.

This change ensures that both Renovate upgrades take place in a single MR.

Instead of duplicates, eg: gitlab-com/runbooks!4701 (closed) and gitlab-com/runbooks!4700 (closed).

cc @pguinoiseau

Edited by Andrew Newdigate

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