Fix OpenStruct use

Fixes OpenStruct use since Ruby 3 discourages it

Changelog: other

.rubocop_manual_todo.yml

@@ -2607,7 +2607,6 @@ Style/OpenStructUse:
     - 'spec/models/design_management/design_at_version_spec.rb'
     - 'spec/models/user_spec.rb'
     - 'spec/presenters/packages/nuget/search_results_presenter_spec.rb'
-    - 'spec/requests/api/graphql/mutations/design_management/delete_spec.rb'
     - 'spec/requests/api/import_github_spec.rb'
     - 'spec/services/packages/nuget/metadata_extraction_service_spec.rb'
     - 'spec/services/projects/import_service_spec.rb'

spec/requests/api/graphql/mutations/design_management/delete_spec.rb

@@ -53,7 +53,7 @@ RSpec.describe "deleting designs" do
 
   context 'the designs list contains filenames we cannot find' do
     it_behaves_like 'a failed request' do
-      let(:designs) { %w/foo bar baz/.map { |fn| OpenStruct.new(filename: fn) } }
+      let(:designs) { %w/foo bar baz/.map { |fn| instance_double('file', filename: fn) } }
       let(:the_error) { a_string_matching %r/filenames were not found/ }
     end
   end