Prepare for the release (Azure#52715)

Author: nick863

sdk/ai/Azure.AI.Agents.Persistent/CHANGELOG.md

@@ -1,16 +1,10 @@
 # Release History
 
-## 1.2.0-beta.5 (Unreleased)
-
-### Features Added
-
-### Breaking Changes
+## 1.2.0-beta.5 (2025-09-18)
 
 ### Bugs Fixed
 - Fix issue with image block serialization [issue](https://github.com/Azure/azure-sdk-for-net/issues/52571)
 
-### Other Changes
-
 ## 1.2.0-beta.4 (2025-09-05)
 
 ### Features Added