Update CHANGELOG.md

Co-authored-by: Emídio Neto <[email protected]>

Author: Ronald-TR

CHANGELOG.md

@@ -6,6 +6,9 @@ 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
+
+## Fixed
+
 - `opentelemetry-instrumentation-aws-lambda` Avoid exception when a handler is not present.
   ([#2750](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2750))