chore(doc): Add missing PR to yamux CHANGELOG.md

Add missing PR to yamux CHANGELOG.md

Pull-Request: #3855.

Author: dariusc93

muxers/yamux/CHANGELOG.md

@@ -2,9 +2,9 @@
 
 - Drop `Yamux` prefix from all types.
   Users are encouraged to import the `yamux` module and refer to types via `yamux::Muxer`, `yamux::Config` etc.
-  See [PR XXXX].
+  See [PR 3852].
 
-[PR XXXX]: https://github.com/libp2p/rust-libp2p/pull/XXXX
+[PR 3852]: https://github.com/libp2p/rust-libp2p/pull/3852
 
 ## 0.43.0