Users without groups should use admin retirement

Backport of ManageIQ#19309

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1754043

app/models/mixins/retirement_mixin.rb

@@ -254,8 +254,12 @@ def valid_zone?
 
   def system_context_requester
     if try(:evm_owner_id).present?
-      if User.find_by(:id => evm_owner_id).present?
+      user = User.find_by(:id => evm_owner_id)
+      if user.present? && user.current_group.present?
         return evm_owner
+      elsif user.present? && !user.current_group.present?
+        $log.info("#{name} has evm_owner present but user has no group so defaulting to admin.")
+        return User.super_admin
       else
         $log.info("#{name} has evm_owner_id present but no user with that id found so defaulting to admin.")
         return User.super_admin