Update 3.13.0 release notes

Author: michaelklishin

release-notes/3.13.0.md

@@ -163,6 +163,14 @@ GET /api/queues` HTTP API endpoint has dropped several rarely used metrics, resu
 A 3.13 RabbitMQ node will fail to boot if the old configuration setting is set.
 For example, if you set `mqtt.subscription_ttl = 3600000` (1 hour) prior to 3.13, replace that setting with `mqtt.max_session_expiry_interval_seconds = 3600` (1 hour) in 3.13.
 
+### rabbitmqctl node_health_check is Now a No-Op
+
+`rabbitmqctl node_health_check` has been deprecated for over three years
+and is now an no-op (does nothing).
+
+See the [Health Checks section](https://www.rabbitmq.com/monitoring.html#health-checks) in the monitoring guide
+to find out what modern alternatives are available.
+
 ### openSUSE Leap Package is not Provided
 
 An openSUSE Leap package will not be provided with this release of RabbitMQ.