update build command to syntax changes in Nix 2.4

.github/workflows/build.yml

@@ -40,6 +40,9 @@ jobs:
       uses: cachix/install-nix-action@v14.1
       with:
         nix_path: "${{ matrix.nixPath }}"
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
     - name: Show nixpkgs version
       run: nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
 #   - name: Setup cachix
@@ -58,8 +61,7 @@ jobs:
           -I nixpkgs=$(nix-instantiate --find-file nixpkgs) \
           -I $PWD
     - name: Build nix packages
-      # TODO switch to default nixpkgs channel once nix-build-uncached 1.0.0 is in stable
-      run: nix run -I 'nixpkgs=channel:nixos-unstable' nixpkgs.nix-build-uncached -c nix-build-uncached ci.nix -A cacheOutputs
+      run: nix shell -f '<nixpkgs>' nix-build-uncached -c nix-build-uncached ci.nix -A cacheOutputs
     - name: Trigger NUR update
       if: ${{ matrix.nurRepo != '<YOUR_REPO_NAME>' }}
       run: curl -XPOST "https://nur-update.herokuapp.com/update?repo=${{ matrix.nurRepo }}"