add changelog entry

Author: suauk

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Handle OTEL_PROPAGATORS contains None
+  ([#4143](https://github.com/open-telemetry/opentelemetry-python/pull/4553))
+
 ## Version 1.32.0/0.53b0 (2025-04-10)
 
 - Fix user agent in OTLP HTTP metrics exporter