Add changelox

Author: xrmx

CHANGELOG.md

@@ -58,6 +58,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4068](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4068))
 - `opentelemetry-instrumentation-mysqlclient`: Replace SpanAttributes with semconv constants
   ([#4067](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4067))
+- `opentelemetry-instrumentation-system-metrics`: Use proper numeric `cpython.gc.generation` attribute in CPython metrics, out of spec`generation` attribute is deprecated and will be removed in the future
+  ([#4092](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4092))
 
 ## Version 1.39.0/0.60b0 (2025-12-03)