[Zendesk Support] How to ignore Side Conversation to assign agent while updating ticket?

Hi,

I created a trigger which updates the assignee of a ticket to the last agent who updated the ticket. 

Recently I discovered, that when a (light) agents replies in a side conversation, the trigger would also be fired and this (light) agent would become the assignee of the ticket.

In the screenshot below you can see the trigger I created and the ANY condition I had in mind, so that a new reply in a side conversation would not fire the trigger.

Unfortunately, the only operator in this condition is IS and there is not IS NOT.

Before I would create a feature request, would any of you know an alternative solution?

Thanks in advance!