ci: fix missing target in publish workflow

.github/workflows/publish.yaml

@@ -3,6 +3,10 @@ name: "Publish"
 on:
   release:
     types: [published]
+  workflow_dispatch:
+
+env:
+  TARGET: rclone_backup
 
 jobs:
   publish:
@@ -28,6 +32,6 @@ jobs:
         with:
           args: |
             --all \
-            --target rclone_backup \
+            --target ${{ env.TARGET }} \
             --image ${{ steps.information.outputs.image }} \
             --docker-hub ${{ steps.information.outputs.repository }}