docs: prepare release 6.3.1

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]
+
+## [6.3.1] - 2025-03-18
 ### Fixed
 - ensure numeric issues in const are correctly evaluated ([#805](https://github.com/jsonrainbow/json-schema/pull/805))
 - fix 6.3.0 regression with comparison of null values during validation ([#806](https://github.com/jsonrainbow/json-schema/issues/806))