Update OpenAI Agents changelog with PR references

Author: nagkumar91

instrumentation-genai/opentelemetry-instrumentation-openai-agents/CHANGELOG.md

@@ -9,3 +9,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Initial barebones package skeleton: minimal instrumentor stub, version module,
   and packaging metadata/entry point.
+  ([#3805](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3805))
+- Implement OpenAI Agents span processing aligned with GenAI semantic conventions.
+  ([#3817](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3817))