Remove subtransaction from DastSite

This changes the service to use regular find_or_create_by so that we
don't start a subtransaction

ee/app/services/dast_sites/find_or_create_service.rb

@@ -7,7 +7,7 @@ module DastSites
     def execute!(url:)
       raise PermissionsError, 'Insufficient permissions' unless allowed?
 
-      find_or_create_by!(url)
+      DastSite.find_or_create_by!(project: project, url: url) # rubocop:disable CodeReuse/ActiveRecord
     end
 
     private
@@ -15,9 +15,5 @@ module DastSites
     def allowed?
       Ability.allowed?(current_user, :create_on_demand_dast_scan, project)
     end
-
-    def find_or_create_by!(url)
-      DastSite.safe_find_or_create_by!(project: project, url: url)
-    end
   end
 end