Update automations.md (#29319)

Author: domalessi

content/en/service_management/on-call/automations.md

@@ -9,6 +9,10 @@ further_reading:
   text: "Workflow Automation"
 ---
 
+{{< site-region region="gov" >}}
+<div class="alert alert-warning">On-Call is not supported for your selected <a href="/getting_started/site">Datadog site</a> ({{< region-param key="dd_site_name" >}}).</div>
+{{< /site-region >}}
+
 ## Overview
 
 Automations allow you to trigger actions based on events in On-Call. There are two types: