N+1 query in spec/requests/api/merge_request_spec.rb

The CE->EE merge failed in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4242 due to https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/49432114.

I verified that this was due to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16626, since the call to MergeRequest#mergeable? incurs additional queries in EE for approvers.

/cc: @oswaldo