Bump Ruby version to 2.7.6
CI has been using 2.7.6 since gitlab-org/gitlab-build-images!518 (merged). GDK is being updated in gitlab-org/gitlab-development-kit!2781 (merged).
Related to https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/7243
CI has been using 2.7.6 since gitlab-org/gitlab-build-images!518 (merged). GDK is being updated in gitlab-org/gitlab-development-kit!2781 (merged).
Related to https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/7243