docs: updated changelog

Author: Yuri Zmytrakov

CHANGELOG.md

@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- Fixed datetime filtering for .0Z milliseconds to preserve precision in apply_filter_datetime, ensuring only items exactly within the specified range are returned. [#535](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/535)
+
 ### Removed
 
 ### Updated