mod: yet more adjustments to workflow file

.gitea/workflows/publish-attic.yaml

@@ -22,10 +22,6 @@ jobs:
 
       - name: Install upstream Nix
         uses: cachix/install-nix-action@v31
-        with:
-          extra_nix_config: |
-            experimental-features = nix-command flakes
-            sandbox = true
 
       - name: Install Attic client
         shell: bash
@@ -53,6 +49,12 @@ jobs:
           attic login --set-default ci "$ATTIC_SERVER" "$ATTIC_TOKEN"
           attic use "$ATTIC_CACHE"
 
+      - name: Prepare builds
+        shell: bash
+        run: |
+          set -euo pipefail
+          sudo rm -rf /homeless-shelter || rm -rf /homeless-shelter
+
       - name: Build packages
         shell: bash
         run: |