fix: use same Nixpkgs as everywhere

Author: fricklerhandwerk

.github/workflows/actionlint.yaml

@@ -24,6 +24,8 @@ jobs:
         with:
           persist-credentials: false # Because installing actionlint runs arbitrary code, we discard the GITHUB_TOKEN after this step
       # Taken from https://github.com/rhysd/actionlint/blob/v1.7.7/docs/usage.md#use-actionlint-on-github-actions
+      - uses: cachix/install-nix-action@v29
       - name: Check workflow files
-        run: nix-shell -p actionlint --run actionlint
-
+        run: |
+          export NIX_PATH=nixpkgs=$(nix-instantiate --eval -A pkgs.path)
+          nix-shell -p actionlint --run actionlint