added new version notes for linux extension

Author: MSFT-Monish

articles/governance/machine-configuration/whats-new/agent.md

@@ -61,6 +61,13 @@ For information on release notes for the connected machine agent, see
 
 ## Extension for Linux extension release notes (Microsoft.GuestConfiguration.ConfigurationforLinux)
 
+### Version 1.26.87 - June 2025
+
+#### Updated
+
+- Updated .NET from version 6 to 8
+- Updated PowerShell from version 7.2.x to 7.4.7
+
 ### Version 1.26.85 - March 2025
 
 #### New Features