chore: update changes

CHANGES-5.0.md

@@ -4,6 +4,7 @@
 
 * Add `cert_common_name` and `cert_subject` placeholder support for authz_http and authz_mongo.[#8973](https://github.com/emqx/emqx/pull/8973)
 * Use milliseconds internally in emqx_delayed to store the publish time, improving precision.[#9060](https://github.com/emqx/emqx/pull/9060)
+* More rigorous checking of flapping to improve stability of the system. [#9136](https://github.com/emqx/emqx/pull/9136)
 
 ## Bug fixes