Changing ActiveRecord to ApplicationRecord in spec

Related Issue: #362031

Changelog: fixed

.rubocop_todo/database/multiple_databases.yml

@@ -4,4 +4,3 @@ Database/MultipleDatabases:
     - 'db/post_migrate/20210317104032_set_iteration_cadence_automatic_to_false.rb'
     - 'db/post_migrate/20210811122206_update_external_project_bots.rb'
     - 'db/post_migrate/20210812013042_remove_duplicate_project_authorizations.rb'
-    - 'ee/spec/services/ee/merge_requests/update_service_spec.rb'

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

@@ -305,7 +305,6 @@ def update_merge_request(opts)
 
     context 'when called inside an ActiveRecord transaction' do
       it 'does not attempt to update code owner approval rules' do
-        allow(ActiveRecord::Base.connection).to receive(:transaction_open?).and_return(true)
         expect(::MergeRequests::SyncCodeOwnerApprovalRulesWorker).not_to receive(:perform_async)
 
         update_merge_request(title: 'Title')