If your email service supports Sieve scripts (for example, Fastmail or Proton Mail), you can use this filter [1] that I made. It's very aggressive and will block all emails that originate from Zendesk, so you'll need to disable it whenever you're actually expecting mail from Zendesk.
[1]: https://gist.github.com/hampuskraft/780c8fbcc4042689153533ef...