Update CHANGELOG.md

Author: xrmx

CHANGELOG.md

@@ -28,6 +28,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4595](https://github.com/open-telemetry/opentelemetry-python/pull/4595))
 - Bump semantic conventions to 1.34.0
   ([#4599](https://github.com/open-telemetry/opentelemetry-python/pull/4599))
+- Drop support for Python 3.8
+  ([#4520](https://github.com/open-telemetry/opentelemetry-python/pull/4520))
 
 ## Version 1.33.0/0.54b0 (2025-05-09)