Remove Ruby 2.7 support
We initially attempted to remove Ruby 2.7 support in https://gitlab.com/gitlab-org/gitlab-exporter/-/merge_requests/192, but we still have some Ruby 2.7 usage in the wild.
Thus we are likely to re-introduce Ruby 2.7 support for gitlab-exporter
in the short term: https://gitlab.com/gitlab-org/gitlab-exporter/-/merge_requests/194.
The underlying issue is that we are pinning omnibus versions on Redis VMs. There is an issue for Reliability to address this, at the very least by bumping the pin and performing a coordinated update (to avoid availability issues): https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/24543.
Once that has been addressed, we should be able to fully remove the Ruby 2.7 support one and for all.