Upload GitHub workflow artifacts even when the test fails.

When a test in `.github/workflows/ci.yml`'s `gpu-test` fails,
ensure that it uploads the artifacts anyway. These are screenshots and
comparison images, so they're valuable in debugging the failure.

.github/workflows/ci.yml

@@ -284,6 +284,7 @@ jobs:
           done
 
       - uses: actions/upload-artifact@v3
+        if: always() # We want artifacts even if the tests fail.
         with:
           name: comparison-images
           path: |