Add warning to scheduled report docs, slack is unsupported in gov (#29271)

Author: tim-higgins-dd

content/en/dashboards/sharing/scheduled_reports.md

@@ -65,6 +65,11 @@ To see the report before saving the schedule, click **Send Test Email**. You can
 
 #### Slack recipients
 
+{{< site-region region="gov" >}}
+
+<div class="alert alert-warning">Slack recipients are not supported for your selected <a href="/getting_started/site">Datadog site</a> ({{< region-param key="dd_site_name" >}}).</div>
+{{< /site-region >}}
+
 To add Slack recipients, select the Slack workspace and channel from the available dropdowns. If you do not see any Slack workspaces available, ensure you have the Datadog [Slack Integration][8] installed. All public channels within the Slack workspace should be listed automatically. To select a private Slack channel, make sure to invite the Datadog Slack bot to the channel in Slack. To send a test message to Slack, add a channel recipient and click **Send Test Message**.
 
 **{{< img src="dashboards/scheduled_reports/add_slack_recipients.png" alt="The configuration modal for editing scheduled report email recipients." style="width:90%;" >}}**