docs: Prepare 6.6.3 release

Author: DannyvdSluijs

CHANGELOG.md

@@ -6,6 +6,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
+## [6.6.3] - 2025-12-02
 ### Changed
 - Restricted `mark-mabe/php-enum` dependency to `^4.4` due to lower versions emitting a warning on PHP 8 ([#854](https://github.com/jsonrainbow/json-schema/pull/854))