docs: Add changelog entry

Author: DannyvdSluijs

CHANGELOG.md

@@ -6,6 +6,9 @@ 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]
+### Added
+- Add return types in the test suite ([#748](https://github.com/jsonrainbow/json-schema/pull/748))
+
 ### Fixed
 - Correct misconfigured mocks in JsonSchema\Tests\Uri\UriRetrieverTest ([#741](https://github.com/jsonrainbow/json-schema/pull/741))
 - Fix pugx badges in README ([#742](https://github.com/jsonrainbow/json-schema/pull/742))