Fix `Rails/WhereExists` cop in lib/tasks (#28852)

.rubocop_todo.yml

@@ -89,7 +89,6 @@ Rails/WhereExists:
     - 'app/services/activitypub/fetch_remote_status_service.rb'
     - 'app/services/vote_service.rb'
     - 'app/workers/move_worker.rb'
-    - 'lib/tasks/tests.rake'
     - 'spec/models/account_spec.rb'
     - 'spec/services/activitypub/process_collection_service_spec.rb'
     - 'spec/services/purge_domain_service_spec.rb'

lib/tasks/tests.rake

@@ -24,7 +24,7 @@ namespace :tests do
         exit(1)
       end
 
-      if Account.where(domain: Rails.configuration.x.local_domain).exists?
+      if Account.exists?(domain: Rails.configuration.x.local_domain)
         puts 'Faux remote accounts not properly cleaned up'
         exit(1)
       end