Update CHANGELOG.md to include JSON schema validation improvements

Author: glichtenstein

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [PR #1496](https://github.com/nf-core/rnaseq/pull/1496) - Template update for nf-core/tools v3.2.0
 - [PR #1499](https://github.com/nf-core/rnaseq/pull/1499) - Bump MultiQC module to 1.27
 - [PR #1508](https://github.com/nf-core/rnaseq/pull/1508) - Fix missing Bracken results in the MultiQC report
+- [PR #1528](https://github.com/nf-core/rnaseq/pull/1528) - Improve JSON schema validation
 
 # 3.18.0 - 2024-12-19