add firewall rule (#5367)

Author: m-nash

.github/workflows/copilot-setup-steps.yml

@@ -15,6 +15,10 @@ jobs:
     permissions:
       contents: read
 
+    env:
+      # Allow Copilot to access Visual Studio assets URLs needed for NuGet restore
+      COPILOT_AGENT_FIREWALL_ALLOW_LIST_ADDITIONS: "vsblob.vsassets.io"
+
     steps:
       - name: Checkout code
         uses: actions/checkout@v4