Copy change log updates from release/v1.21.x-0.42bx (#3517)

Author: opentelemetrybot

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
-## Version 1.21.0/0.42b0 (2023-11-01)
+## Version 1.21.0/0.42b0 (2023-11-07)
 
 - Fix `SumAggregation`
   ([#3390](https://github.com/open-telemetry/opentelemetry-python/pull/3390))