fix changelog

Author: hgiasac

CHANGELOG.md

@@ -4,7 +4,7 @@ This changelog documents the changes between release versions.
 ## [Unreleased]
 Changes to be included in the next upcoming release
 
-## 0.2.1 - 2025.08.15
+## [0.2.1] - 2025.08.15
 * Use `ndc-sdk-python` package version `v0.40`
 
 ## [0.2.0] - 2025-04-02