use a different destination folder for PR

Author: deniak

.github/workflows/pr-merged.yml

@@ -7,7 +7,7 @@ jobs:
   delete_assets:
     runs-on: ubuntu-latest
     env:
-      destination: assets/website-2021/pr-${{ github.event.number }}/
+      destination: assets/website-2021-dev/pr-${{ github.event.number }}/
     steps:
       - name: Delete PR assets from the cdn-dev.w3.org bucket
         if: success()