Fix the package project url (#1052)

Co-authored-by: Mark Wallace <markwallace@microsoft.com>

Author: markwallace-microsoft

dotnet/nuget/nuget-package.props

@@ -35,7 +35,7 @@
     <!-- Required license, copyright, and repo information. Packages can override. -->
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <Copyright>© Microsoft Corporation. All rights reserved.</Copyright>
-    <PackageProjectUrl>https://aka.ms/tbd</PackageProjectUrl>
+    <PackageProjectUrl>https://learn.microsoft.com/agent-framework/</PackageProjectUrl>
     <RepositoryUrl>https://github.com/microsoft/agent-framework</RepositoryUrl>
     <PublishRepositoryUrl>true</PublishRepositoryUrl>