Alerting: Fix notifications for Microsoft Teams (#53810)

This commit fixes notifications for Microsoft Teams where notifications
would just contain "Card" rather than the title.

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -2229,6 +2229,7 @@ var expNonEmailNotifications = map[string][]string{
 			  "contentType": "application/vnd.microsoft.card.adaptive"
 		    }
 		  ],
+		  "summary": "[FIRING:1] TeamsAlert (default)",
 		  "type": "message"
 		}`,
 	},