Prepare 16.8.4 release for omnibus-gitlab-jh

Release issue: https://jihulab.com/gitlab-cn/release/tasks/-/issues/142

Summary

This MR prepares 16-8-stable-jh for 16.8.4.

Automated cherry-picking

Merge requests labeled ~"Pick into 16.8" should be automatically picked into this MR.

Manual intervention

If merge requests cannot be picked automatically they have to be created manually targeting 16-8-stable-jh-patch-4.

---

See also Patch Releases documentation.