Update dependency zeitwerk to '~> 2.6', '>= 2.6.13'

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144173



Merged-by: Mark Lapierre <mlapierre@gitlab.com>
Approved-by: Mark Lapierre <mlapierre@gitlab.com>
Co-authored-by: GitLab Renovate Bot <gitlab-bot@gitlab.com>