chore(etna): disable attic

just unused, adds yet another thing to compile so i don't really see the
point anymore

.github/workflows/ci.yml

@@ -31,12 +31,11 @@ jobs:
       - uses: actions/checkout@v4
       - uses: DeterminateSystems/nix-installer-action@v9
 
-      - name: setup attic
-        uses: ryanccn/attic-action@v0
+      - name: setup cachix
+        uses: cachix/cachix-action@v13
         with:
-          endpoint: https://attic.uku3lig.net
-          cache: uku
-          token: ${{ secrets.ATTIC_TOKEN }}
+          name: uku3lig
+          authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
       - name: build
         run: nix build -L --accept-flake-config .#${{ matrix.pkg }}