Remove subtransactions from OnboardingProgress

This is only called when a root group is created so we don't need to use
safe_find_or_create_by

app/models/onboarding_progress.rb

@@ -45,7 +45,7 @@ class OnboardingProgress < ApplicationRecord
     def onboard(namespace)
       return unless root_namespace?(namespace)
 
-      safe_find_or_create_by(namespace: namespace)
+      create(namespace: namespace)
     end
 
     def onboarding?(namespace)