Binary cache on GitHub Pages

Hi,
I would like to build a small binary cache served by GitHub pages.

At the moment I have an action:

name: Build

on:
  push:

jobs:
  build:
    runs-on: ubuntu-latest
    permissions:
      id-token: write
      pages: write
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4.1.7

      - name: Install Nix
        uses: cachix/install-nix-action@v27
        with:
          nix_path: nixpkgs=channel:nixos-unstable

      - name: Build Nix package
        run: nix-build

      - name: Export Nix store paths
        run: |
          mkdir -p cache
          nix-store --query --requisites ./result
          nix-store --export $(nix-store --query --requisites ./result) >cache/cache.nar

      - name: Create nix-cache-info file
        run: |
          cat <<EOF | tee cache/nix-cache-info
          StoreDir: /nix/store
          WantMassQuery: 1
          Priority: 30
          EOF

      - name: Create .narinfo file
        run: |
          STORE_PATH=$(nix-store --query ./result)
          FILE_SIZE=$(stat -c%s cache/cache.nar)
          cat <<EOF | tee cache/${STORE_PATH##*/}.narinfo
          StorePath: ${STORE_PATH}
          URL: nar/${STORE_PATH##*/}.nar
          Compression: none
          FileHash: $(nix-hash --flat --type sha256 cache/cache.nar)
          FileSize: $FILE_SIZE
          NarHash: $(nix-hash --flat --type sha256 cache/cache.nar)
          NarSize: $FILE_SIZE
          EOF
          mkdir cache/nar
          cp cache/cache.nar cache/nar/${STORE_PATH##*/}.nar

      - name: Setup Pages
        uses: actions/configure-pages@v5.0.0

      - name: Upload artifact
        uses: actions/upload-pages-artifact@v3.0.1
        with:
          path: ./cache

      - name: Deploy to GitHub Pages
        uses: actions/deploy-pages@v4.0.5

If I try:

nix-channel --add https://github.com/<>/<>/archive/main.tar.gz mynix
nix-channel --update

nix-env --install --attr mynix.my-go --substituters https://<>.github.io/<>

it tries to build the package.

Instead if I manually download and import the nar cache:

curl -LO https://<>.github.io/<>/cache.nar
nix-store --import <cache.nar

nix-env --install --attr mynix.my-go

The package is just installed without build.

Any suggestions?

Thanks