Stop checking codeowner changes on MR refresh for deleted branch

Issue:
MR:

ee/app/services/ee/merge_requests/refresh_service.rb

@@ -49,6 +49,8 @@ module EE
       end
 
       def code_owners_updated?
+        return if push.branch_removed?
+
         push.modified_paths.find { |path| ::Gitlab::CodeOwners::FILE_PATHS.include?(path) }
       end
 

ee/spec/services/ee/merge_requests/refresh_service_spec.rb

@@ -122,6 +122,12 @@ RSpec.describe MergeRequests::RefreshService do
 
             it_behaves_like 'does not refresh the code owner rules'
           end
+
+          context 'when the branch is deleted' do
+            let(:newrev) { Gitlab::Git::BLANK_SHA }
+
+            it_behaves_like 'does not refresh the code owner rules'
+          end
         end
 
         context 'when the branch is not protected' do