Add UV_TORCH_BACKEND environment variable to CI job

Author: bhimrazy

.github/workflows/ci-testing.yml

@@ -32,6 +32,7 @@ jobs:
     timeout-minutes: 35
     env:
       TORCH_URL: "https://download.pytorch.org/whl/cpu/torch_stable.html"
+      UV_TORCH_BACKEND: "cpu"
 
     steps:
       - uses: actions/checkout@v6