[#1331] Update changelog

Author: elfenpiff

doc/release-notes/iceoryx2-unreleased.md

@@ -49,6 +49,8 @@
 * Replace `lazy_static` dependency with `LazyLock` from `std` in `std` builds or
   a custom minimal spin-based implementation for `no_std` builds
   [#1321](https://github.com/eclipse-iceoryx/iceoryx2/issues/1321)
+* `CleanupState` implements `ZeroCopySend`
+  [#1331](https://github.com/eclipse-iceoryx/iceoryx2/issues/1331)
 
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