docs: Update CHANGELOG.md for PR #874

Author: github-actions[bot]

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - UriRetriever: Include actual media type in InvalidSchemaMediaTypeException message ([#872](https://github.com/jsonrainbow/json-schema/pull/872))
 - docs: Correct trailing spaces in Markdown ([#873](https://github.com/jsonrainbow/json-schema/pull/873))
 
+### Added
+- Automate changelog updates on PR merge ([#874](https://github.com/jsonrainbow/json-schema/pull/874))
+
 ## [6.6.4] - 2025-12-19
 ### Changed
 - ci: Run workflows against 5.x.x branches ([#859](https://github.com/jsonrainbow/json-schema/pull/859))