ci: run the workflow as a dry run first

- a manually triggered first run in CI uploads the full list of manifests to delete
- a later pull request makes the workflow hourly again

.github/workflows/clean-manifests.yaml

@@ -1,8 +1,6 @@
 name: Clean manifests
 
 on:
-  schedule:
-    - cron: "20 * * * *"
   workflow_dispatch:
 
 permissions: {}
@@ -34,18 +32,18 @@ jobs:
         with:
           persist-credentials: false
 
-      - name: Delete the unused manifests
+      - name: List the manifests to delete
         env:
           GH_TOKEN: ${{ secrets.GHCR_CLEANUP_TOKEN }}
           DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_CLEANUP_USERNAME }}
           DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_CLEANUP_TOKEN }}
-        run: scripts/clean-manifests.sh --delete 200
+        run: scripts/clean-manifests.sh
 
-      - name: Upload the list of deleted manifests
+      - name: Upload the list of manifests to delete
         if: ${{ always() }}
         uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
         with:
-          name: deleted-manifests
-          path: scripts/deleted-manifests.tsv
+          name: manifests-to-delete
+          path: scripts/manifests-to-delete.tsv
           if-no-files-found: ignore
           retention-days: 90