Test gap: rebase MR with remove approvals settings

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In gitlab-com/gl-infra/production#8608 (closed) some users were experiencing 500 errors after rebasing their MRs when their projects had the Remove all approvals setting on.

The user flow that caused the 500 errors (to be confirmed):

1. Create project -> Remove all approvals setting on (this may be default) / FF merge on
2. Create MR (ensure target has at least one more commit than source)
3. Approve MR
4. Rebase <- this never completes and this is where the 500 occurs
5. Check approval removed (may have to wait 10s and refresh as removing approvals is async)
6. Approve MR
7. Check approval NOT removed as it is a rebase
8. Merge

There are two scenarios where this can occur based on the following settings:

1. Remove all approvals
2. Remove approvals of Code owners

This issue is to ensure we are covering this scenario with either feature specs or an E2E test.

Incident:

• 2023-03-28: MRs stuck with 500 graphql errors (gitlab-com/gl-infra/production#8608 - closed)
• Incident Review: MRs stuck with 500 graphql errors (gitlab-com/gl-infra/production#8670 - closed)