ci: set target fx [skip-ci]

Author: MIchaelMainer

dotnet/src/Microsoft.Agents.M365Copilot/Microsoft.Agents.M365Copilot.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;net6.0;net7.0;net8.0;</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net8.0;net9.0;</TargetFrameworks>
     <Description>Microsoft 365 Copilot APIs v1.0 client library enables you to call the Microsoft 365 Copilot APIs in your applications and custom engine agents.</Description>
     <Copyright>© Microsoft Corporation. All rights reserved.</Copyright>
     <AssemblyTitle>Microsoft Agents M365 Copilot APIs v1.0 Client Library</AssemblyTitle>