[ContentUnderstanding] Set 1.2.0b2 release date to 2026-06-10 (#47447)

Author: chienyuanchang

sdk/contentunderstanding/azure-ai-contentunderstanding/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.2.0b2 (Unreleased)
+## 1.2.0b2 (2026-06-10)
 
 ### Bugs Fixed
 - Filtered service-emitted `LLMStats:` telemetry entries from the rendered `rai_warnings` front matter.