changelog for 6.15.3

Author: baszoetekouw

CHANGELOG.md

@@ -5,7 +5,7 @@ We will continue to post relevant release notes on the GitHub release page. More
 
 More information about our release strategy can be found in the [Development Guidelines](https://github.com/OpenConext/OpenConext-engineblock/wiki/Development-Guidelines#release-notes) on the EngineBlock wiki.
 
-## 6.15.3-beta
+## 6.15.3
 Maintenance:
   * Upgrade saml2 library