Update swarm/CHANGELOG.md

Author: thomaseizinger

swarm/CHANGELOG.md

@@ -4,10 +4,10 @@
   See [PR 3715].
 
 - Return a bool from `ExternalAddresses::on_swarm_event` and `ListenAddresses::on_swarm_event` indicating whether any state was changed.
-  See [PR XXXX].
+  See [PR 3865].
 
 [PR 3715]: https://github.com/libp2p/rust-libp2p/pull/3715
-[PR XXXX]: https://github.com/libp2p/rust-libp2p/pull/XXXX
+[PR 3865]: https://github.com/libp2p/rust-libp2p/pull/3865
 
 ## 0.42.2