ci: group ruby-version updates together
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