Update changelog.

Author: michaelsafyan

instrumentation-genai/opentelemetry-instrumentation-google-genai/CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Restructure tests to keep in line with repository conventions ([#3344](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3344))
 
+- Fix [bug](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/3416) where
+span attribute `gen_ai.response.finish_reasons` is empty ([#3417](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3417))
+
 ## Version 0.1b0 (2025-03-05)
 
 - Add support for async and streaming.