Update changelog

Author: devonh

CHANGES.md

@@ -10,6 +10,7 @@ Please check [the relevant section in the upgrade notes](https://github.com/elem
 - Add ability to configure forward/outbound proxy via homeserver config instead of environment variables. See `http_proxy`, `https_proxy`, `no_proxy_hosts`. ([\#18686](https://github.com/element-hq/synapse/issues/18686))
 - Advertise experimental support for [MSC4306](https://github.com/matrix-org/matrix-spec-proposals/pull/4306) (Thread Subscriptions) through `/_matrix/clients/versions` if enabled. ([\#18722](https://github.com/element-hq/synapse/issues/18722))
 - Stabilise support for delegating authentication to [Matrix Authentication Service](https://github.com/element-hq/matrix-authentication-service/). ([\#18759](https://github.com/element-hq/synapse/issues/18759))
+- Implement the push rules for experimental [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-doc/issues/4306). ([\#18762](https://github.com/element-hq/synapse/issues/18762))
 
 ### Bugfixes
 
@@ -44,6 +45,7 @@ Please check [the relevant section in the upgrade notes](https://github.com/elem
 - Prevent "Move labelled issues to correct projects" GitHub Actions workflow from failing when an issue is already on the project board. ([\#18755](https://github.com/element-hq/synapse/issues/18755))
 - Bump minimum supported Rust version (MSRV) to 1.82.0. Missed in [#18553](https://github.com/element-hq/synapse/pull/18553) (released in Synapse 1.134.0). ([\#18757](https://github.com/element-hq/synapse/issues/18757))
 - Make `Clock.sleep(...)` return a coroutine, so that mypy can catch places where we don't await on it. ([\#18772](https://github.com/element-hq/synapse/issues/18772))
+- Update implementation of [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-doc/issues/4306) to include automatic subscription conflict prevention as introduced in later drafts. ([\#18756](https://github.com/element-hq/synapse/issues/18756))