Prepare 16.6.8 release for omnibus-gitlab-jh

Release issue: https://jihulab.com/gitlab-cn/release/tasks/-/issues/184

Summary

This MR prepares 16-6-stable-jh for 16.6.8.

Automated cherry-picking

Merge requests labeled ~"Pick into 16.6" should be automatically picked into this MR.

Manual intervention

If merge requests cannot be picked automatically they have to be created manually targeting 16-6-stable-jh-patch-8.

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See also Patch Releases documentation.