ci: fetch installer directly from hydra

.github/workflows/test.yml

@@ -116,18 +116,9 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
-    - id: latest_installer
-      name: Fetch latest installer from Hydra
-      run: |
-        build_id=$(curl --header 'Accept: application/json' --location --silent \
-          https://hydra.nixos.org/job/nix/master/installerScript/latest-finished \
-          | jq -r '.id')
-        install_url="https://hydra.nixos.org/build/$build_id/download/1/install"
-        echo "install_url=$install_url" >> $GITHUB_OUTPUT
-
-    - uses: cachix/install-nix-action@V30
+    - uses: cachix/install-nix-action@v30
       with:
-        install_url: ${{ steps.latest_installer.outputs.install_url }}
+        install_url: https://hydra.nixos.org/job/nix/master/installerScript/latest-finished/download/1/install
         install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
 
     - run: yarn install --frozen-lockfile