Can't push some branches to GitLab -- "Deny updating a hidden ref"
The same happens for many different repositories:
zen@tails ~/jenkins-jobs.git> (BARE:master) git push --mirror gitlab
Total 0 (delta 0), reused 0 (delta 0)
To gitlab.tails.boum.org:tails/jenkins-jobs
! [remote rejected] gitlab/SponsorS-leftovers -> gitlab/SponsorS-leftovers (deny updating a hidden ref)
! [remote rejected] gitlab/bugfix-15993-adjust-ci-for-usb-images -> gitlab/bugfix-15993-adjust-ci-for-usb-images (deny updating a hidden ref)
! [remote rejected] gitlab/bugfix/11557-rotate-latest-ISO-symlinks -> gitlab/bugfix/11557-rotate-latest-ISO-symlinks (deny updating a hidden ref)
! [remote rejected] gitlab/bugfix/12577-cleanup-build-jobs-leftovers -> gitlab/bugfix/12577-cleanup-build-jobs-leftovers (deny updating a hidden ref)
! [remote rejected] gitlab/bugfix/12599-rake-task-removing-tails-builder-volumes -> gitlab/bugfix/12599-rake-task-removing-tails-builder-volumes (deny updating a hidden ref)
! [remote rejected] gitlab/bugfix/12637-all-build-jobs-cleanup-libvirt-volumes -> gitlab/bugfix/12637-all-build-jobs-cleanup-libvirt-volumes (deny updating a hidden ref)
! [remote rejected] gitlab/feature/10119-adapt-job-generation-script -> gitlab/feature/10119-adapt-job-generation-script (deny updating a hidden ref)
! [remote rejected] gitlab/feature/10287-limited-email-notifications -> gitlab/feature/10287-limited-email-notifications (deny updating a hidden ref)
! [remote rejected] gitlab/feature/11355-reenable-jenkins-notifications -> gitlab/feature/11355-reenable-jenkins-notifications (deny updating a hidden ref)
! [remote rejected] gitlab/feature/12633-lower-reproducible-builds-workload -> gitlab/feature/12633-lower-reproducible-builds-workload (deny updating a hidden ref)
! [remote rejected] gitlab/feature/12654-more-build-env-variations-for-RB-tests -> gitlab/feature/12654-more-build-env-variations-for-RB-tests (deny updating a hidden ref)
! [remote rejected] gitlab/feature/9597-jenkins-share-artifacts-between-jobs -> gitlab/feature/9597-jenkins-share-artifacts-between-jobs (deny updating a hidden ref)
! [remote rejected] gitlab/feature/reboot-after-testing -> gitlab/feature/reboot-after-testing (deny updating a hidden ref)
! [remote rejected] gitlab/feature/reboot-after_post_build_trigger -> gitlab/feature/reboot-after_post_build_trigger (deny updating a hidden ref)
! [remote rejected] gitlab/jenkins2 -> gitlab/jenkins2 (deny updating a hidden ref)
! [remote rejected] gitlab/master -> gitlab/master (deny updating a hidden ref)
! [remote rejected] immerda/bugfix/11557-rotate-latest-ISO-symlinks -> immerda/bugfix/11557-rotate-latest-ISO-symlinks (deny updating a hidden ref)
! [remote rejected] immerda/bugfix/12577-cleanup-build-jobs-leftovers -> immerda/bugfix/12577-cleanup-build-jobs-leftovers (deny updating a hidden ref)
! [remote rejected] immerda/bugfix/12599-rake-task-removing-tails-builder-volumes -> immerda/bugfix/12599-rake-task-removing-tails-builder-volumes (deny updating a hidden ref)
! [remote rejected] immerda/bugfix/12637-all-build-jobs-cleanup-libvirt-volumes -> immerda/bugfix/12637-all-build-jobs-cleanup-libvirt-volumes (deny updating a hidden ref)
! [remote rejected] immerda/feature/10119-adapt-job-generation-script -> immerda/feature/10119-adapt-job-generation-script (deny updating a hidden ref)
! [remote rejected] immerda/feature/10287-limited-email-notifications -> immerda/feature/10287-limited-email-notifications (deny updating a hidden ref)
! [remote rejected] immerda/feature/11355-reenable-jenkins-notifications -> immerda/feature/11355-reenable-jenkins-notifications (deny updating a hidden ref)
! [remote rejected] immerda/feature/12633-lower-reproducible-builds-workload -> immerda/feature/12633-lower-reproducible-builds-workload (deny updating a hidden ref)
! [remote rejected] immerda/feature/12654-more-build-env-variations-for-RB-tests -> immerda/feature/12654-more-build-env-variations-for-RB-tests (deny updating a hidden ref)
! [remote rejected] immerda/feature/9597-jenkins-share-artifacts-between-jobs -> immerda/feature/9597-jenkins-share-artifacts-between-jobs (deny updating a hidden ref)
! [remote rejected] immerda/feature/reboot-after-testing -> immerda/feature/reboot-after-testing (deny updating a hidden ref)
! [remote rejected] immerda/feature/reboot-after_post_build_trigger -> immerda/feature/reboot-after_post_build_trigger (deny updating a hidden ref)
! [remote rejected] immerda/master -> immerda/master (deny updating a hidden ref)
error: failed to push some refs to 'git@gitlab.tails.boum.org:tails/jenkins-jobs'