docs(CHANGELOG.md): move Poseidon hashing performance improvement not…

…e to 'Unreleased' section

This change is made to correctly reflect the status of the improvement, as it has not been released yet.

CHANGELOG.md

@@ -17,6 +17,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased](https://github.com/o1-labs/o1js/compare/be748e42e...HEAD)
 
+### Changed
+
+- Improve performance of Poseidon hashing by a factor of 13x https://github.com/o1-labs/o1js/pull/1378
+
 ## [0.15.3](https://github.com/o1-labs/o1js/compare/1ad7333e9e...be748e42e)
 
 ### Breaking changes
@@ -34,10 +38,6 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Fix approving of complex account update layouts https://github.com/o1-labs/o1js/pull/1364
 
-### Changed
-
-- Improve performance of Poseidon hashing by a factor of 13x https://github.com/o1-labs/o1js/pull/1378
-
 ## [0.15.2](https://github.com/o1-labs/o1js/compare/1ad7333e9e...08ba27329)
 
 ### Fixed