store mimeExtension.js file in artifacts for debugging

Author: emilykl

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

@@ -43,6 +43,7 @@ jobs:
         jupyter labextension build --show-config-json .
         npm run build
         npm ls
+        cp lib/mimeExtension.js ../plotly/labextension/mimeExtension.js
     - name: Check JupyterLab build artifacts
       run: |
         # 1. Hash contents of all static files, sort by content hash
@@ -71,7 +72,6 @@ jobs:
         else
         echo "✅ Build artifacts match expected output (ignoring known 'load' hash in package.json)."
         fi
-
     - name: Store the build artifacts from plotly/labextension
       uses: actions/upload-artifact@v4
       if: failure()