Prepare azure-ai-agentserver-githubcopilot 1.0.0b2 for release (#46522)

Update changelog release date to 2026-04-24.

Co-authored-by: root <root@CPC-cearl-W9ZSG.localdomain>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

sdk/agentserver/azure-ai-agentserver-githubcopilot/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.0.0b2 (Unreleased)
+## 1.0.0b2 (2026-04-24)
 
 ### Breaking Changes