Add Changelog

Author: Punit Maheshwari

instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md

@@ -6,6 +6,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+- Fix `AttributeError` when handling `LegacyAPIResponse` (from `with_raw_response`)
+  ([#4002](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/4002))
 
 ## Version 2.2b0 (2025-11-25)