Use harmonia instead of attic for binary cache

.gitea/workflows/ci.yaml

@@ -23,19 +23,17 @@ jobs:
 
             extra-substituters = https://nix-cache.nul.ie/main
             extra-trusted-public-keys = main:mMChkG8LwXrFirVfudqjSHasK1jV31OVElYD3eImYl8=
-      - name: Set up attic
-        run: |
-          nix run .#nixpkgs.mine.x86_64-linux.attic-client -- \
-            login --set-default colony https://nix-cache.nul.ie "${{ secrets.NIX_CACHE_TOKEN }}"
 
       - name: Check flake
-        run: nix flake check
+        run: nix flake check --no-build
       - name: Build the world
         id: build
         run: |
           path=$(nix build --no-link .#ci.x86_64-linux --json | jq -r .[0].outputs.out)
           echo "path=$path" >> "$GITHUB_OUTPUT"
+
       - name: Push to cache
+        env:
+          HARMONIA_SSH_KEY: ${{ secrets.HARMONIA_SSH_KEY }}
         run: |
-          nix run .#nixpkgs.mine.x86_64-linux.attic-client -- \
-            push main ${{ steps.build.outputs.path }}
+          ci/push-to-cache.sh "${{ steps.build.outputs.path }}"