Prepare 15.9.1 release for cng-jh

Release issue: https://jihulab.com/gitlab-cn/release/tasks/-/issues/43

Summary

This MR prepares 15-9-stable-jh for 15.9.1.

Automated cherry-picking

Merge requests labeled ~"Pick into 15.9" should be automatically picked into this MR.

Manual intervention

If merge requests cannot be picked automatically they have to be created manually targeting 15-9-stable-jh-patch-1.

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See also Patch Releases documentation.