Update CHANGELOG.md (#40643)

Author: ChenxiJiang333

sdk/servicebus/azure-mgmt-servicebus/CHANGELOG.md

@@ -3,7 +3,7 @@
 ## 9.0.0 (2025-04-22)
 
 ### Breaking Changes
-
+  - Removed subfolders of some unused Api-Versions for smaller package size. If your application requires a specific and non-latest Api-Version, it's recommended to pin this package to the previous released version; If your application always only use latest Api-Version, please ignore this change.
   - Removed operation group EventHubsOperations
   - Removed operation group PremiumMessagingRegionsOperations
   - Removed operation group RegionsOperations