Fix .NET package version props generation (#1387)

Generate the Copilot CLI version props before NuGet collects package files so the generated props file is included in the packed build assets.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

dotnet/src/GitHub.Copilot.SDK.csproj

@@ -68,7 +68,7 @@
         <Error Condition="'$(CopilotCliVersion)' == ''" Text="CopilotCliVersion could not be read from nodejs/package-lock.json" />
     </Target>
 
-    <Target Name="_GenerateVersionProps" DependsOnTargets="_GetCopilotCliVersion" BeforeTargets="Pack">
+    <Target Name="_GenerateVersionProps" DependsOnTargets="_GetCopilotCliVersion" BeforeTargets="_GetPackageFiles">
         <PropertyGroup>
             <_VersionPropsContent>
                 <![CDATA[<Project>