Fix artifact upload

Author: marthacryan

.github/workflows/check-js-build.yml

@@ -1,5 +1,5 @@
 on:
-    push:
+    pull_request:
         paths:
         - 'js/**'
         - 'plotly/labextension/**'
@@ -67,6 +67,7 @@ jobs:
 
     - name: Store the build artifacts from plotly/labextension
       uses: actions/upload-artifact@v4
+      if: failure()
       with:
         name: labextension
         path: plotly/labextension