test(windows): missing cu prefix in pytorch index-url

Author: mfuntowicz

.github/workflows/build_kernel_windows.yaml

@@ -57,7 +57,7 @@ jobs:
           cache: 'pip'
 
       - name: Install PyTorch
-        run: pip install torch --index-url https://download.pytorch.org/whl/${{ matrix.torch.wheel }}
+        run: pip install torch --index-url https://download.pytorch.org/whl/cu${{ matrix.torch.wheel }}
 
       - name: Build activation kernel
         run: ( scripts\windows\builder.ps1 -SourceFolder examples/activation -BuildConfig Release -Backend cuda -Build -Force )