Approvals are lost after a `rebase & merge` action fails.

https://gitlab.zendesk.com/agent/tickets/16070

If you use the workflow of rebasing the branch before merging, and you use the approvers features, it seems that the approvals get lost after rebasing fails for whatever reason, making it impossible to manually rebase and merge through the WebUI without the approvers re-approving everything again.

@vsizov can you investigate why this is happening?

/cc @DouweM