Sync code owners rules on MR update

That will help us to show correct code owners rules when
target branch is updated

ee/app/services/ee/merge_requests/update_service.rb

@@ -42,6 +42,13 @@ module EE
 
       private
 
+      override :after_update
+      def after_update(merge_request)
+        super
+
+        ::MergeRequests::SyncCodeOwnerApprovalRules.new(merge_request).execute
+      end
+
       override :create_branch_change_note
       def create_branch_change_note(merge_request, branch_type, old_branch, new_branch)
         super

ee/changelogs/unreleased/security-id-fix-bypass-code-owners.yml

+---
+title: Sync code owners rules on MR update
+merge_request: 1003
+author:
+type: security

ee/spec/services/ee/merge_requests/update_service_spec.rb

@@ -322,5 +322,13 @@ RSpec.describe MergeRequests::UpdateService, :mailer do
         it_behaves_like 'undeletable existing approval rules'
       end
     end
+
+    it 'updates code owner approval rules' do
+      expect_next_instance_of(::MergeRequests::SyncCodeOwnerApprovalRules) do |instance|
+        expect(instance).to receive(:execute)
+      end
+
+      update_merge_request(title: 'Title')
+    end
   end
 end