Fix Style/OpenStructUse offense for Gitlab::Database::Migrations::Runner

Changelog: other

.rubocop_todo/style/open_struct_use.yml

@@ -28,7 +28,6 @@ Style/OpenStructUse:
   - spec/helpers/profiles_helper_spec.rb
   - spec/initializers/doorkeeper_spec.rb
   - spec/lib/gitlab/auth/o_auth/provider_spec.rb
-  - spec/lib/gitlab/database/migrations/runner_spec.rb
   - spec/lib/gitlab/gitaly_client/blobs_stitcher_spec.rb
   - spec/lib/gitlab/gitaly_client/diff_stitcher_spec.rb
   - spec/lib/gitlab/legacy_github_import/project_creator_spec.rb

spec/lib/gitlab/database/migrations/runner_spec.rb

@@ -28,7 +28,7 @@ RSpec.describe Gitlab::Database::Migrations::Runner do
     allow(ActiveRecord::Migrator).to receive(:new) do |dir, _all_migrations, _schema_migration_class, version_to_migrate|
       migrator = double(ActiveRecord::Migrator)
       expect(migrator).to receive(:run) do
-        migration_runs << OpenStruct.new(dir: dir, version_to_migrate: version_to_migrate)
+        migration_runs << double('migrator', dir: dir, version_to_migrate: version_to_migrate)
       end
       migrator
     end