Add changelog

Author: xrmx

CHANGELOG.md

@@ -32,6 +32,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#2901])(https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2901)
 - `opentelemetry-instrumentation-system-metrics` Update metric units to conform to UCUM conventions.
   ([#2922](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2922))
+- `opentelemetry-instrumentation-celery` Don't detach context without a None token
+  ([#2927](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2927))
 
 ### Breaking changes