Fix `Copy Packages` step (#31790)

Resolve issue present
[here.](https://dev.azure.com/azure-sdk/public/_build/results?buildId=4332852&view=logs&j=3dc8fd7e-4368-5a92-293e-d53cefc8c4b3&t=25f5bbca-262e-5e46-5cac-451228cdef01)

eng/pipelines/templates/steps/build.yml

@@ -84,8 +84,7 @@ steps:
       ServiceDirectory: ${{parameters.ServiceDirectory}}
 
   - pwsh: |
-      $artifacts = Get-ChildItem -Recurse -Force "$(Build.ArtifactStagingDirectory)/PackageInfo/*.json" `
-          | ForEach-Object { $_.Name.Replace(".json", "") }
+      $artifacts = "$(ArtifactPackageNames)".Split(",")
 
       foreach ($artifact in $artifacts)
       {