Fix AccessDeniedError in Compliance Dashboard seed

This removes logic that chooses an arbitrary maintainer in favor of
what was previously the fallback logic that chooses an arbitrary admin.
The thinking is that this simplifies the code in favor of logic that
should be more reliable overall.

ee/db/fixtures/development/32_compliance_dashboard_merge_requests.rb

@@ -9,6 +9,10 @@ class Gitlab::Seeder::ComplianceDashboardMergeRequests
     @project = project
   end
 
+  def admin
+    @admin ||= create(:user, :admin)
+  end
+
   def seed!
     used_statuses = []
 
@@ -54,10 +58,8 @@ class Gitlab::Seeder::ComplianceDashboardMergeRequests
       state: :opened
     }
 
-    maintainer = @project.team.maintainers.sample || User.admins.first
-
     Sidekiq::Worker.skipping_transaction_check do
-      merge_request = MergeRequests::CreateService.new(@project, maintainer, opts).execute
+      merge_request = MergeRequests::CreateService.new(@project, admin, opts).execute
       merge_request.save!
       merge_request.approvals.create(approvals)
       merge_request.state = :merged