"Merge when pipeline succeeds" visible if approvals are pending

Originally filed in CE (https://gitlab.com/gitlab-org/gitlab-ce/issues/27019) by @mburtscher

Summary

Even if approvals are missing (configured: at least 1 / actual: 0) the button "Merge when pipeline succeeds" is visible. Clicking it fails with "Something went wrong…"

The "Merge" button (if there is no pending pipeline) is not visible if approvals are missing

Steps to reproduce

Create a project with both pipelines enabled and required approvals for merging. Create a pull-request.

Expected behavior

Button "Merge when pipeline succeeds" should not be visible.

Actual behavior

Button is visible, clicking it will cause an error.

cc: @grzesiek