ci: enable experimental installer tests

Author: getchoo

.github/workflows/ci.yml

@@ -135,9 +135,19 @@ jobs:
           - scenario: on ubuntu
             runs-on: ubuntu-24.04
             os: linux
+            experimental-installer: false
           - scenario: on macos
             runs-on: macos-14
             os: darwin
+            experimental-installer: false
+          - scenario: on ubuntu (experimental)
+            runs-on: ubuntu-24.04
+            os: linux
+            experimental-installer: true
+          - scenario: on macos (experimental)
+            runs-on: macos-14
+            os: darwin
+            experimental-installer: true
     name: installer test ${{ matrix.scenario }}
     runs-on: ${{ matrix.runs-on }}
     steps:
@@ -149,11 +159,22 @@ jobs:
         path: out
     - name: Looking up the installer tarball URL
       id: installer-tarball-url
-      run: echo "installer-url=file://$GITHUB_WORKSPACE/out" >> "$GITHUB_OUTPUT"
+      run: |
+        echo "installer-url=file://$GITHUB_WORKSPACE/out" >> "$GITHUB_OUTPUT"
+        TARBALL_PATH="$(find "$GITHUB_WORKSPACE/out" -name 'nix*.tar.xz' -print | head -n 1)"
+        echo "tarball-path=file://$TARBALL_PATH" >> "$GITHUB_OUTPUT"
     - uses: cachix/install-nix-action@v31
+      if: ${{ !matrix.experimental-installer }}
       with:
         install_url: ${{ format('{0}/install', steps.installer-tarball-url.outputs.installer-url) }}
         install_options: ${{ format('--tarball-url-prefix {0}', steps.installer-tarball-url.outputs.installer-url) }}
+    - uses: ./.github/actions/install-nix-action
+      if: ${{ matrix.experimental-installer }}
+      with:
+        dogfood: false
+        experimental-installer: true
+        tarball_url: ${{ steps.installer-tarball-url.outputs.tarball-path }}
+        github_token: ${{ secrets.GITHUB_TOKEN }}
     - run: sudo apt install fish zsh
       if: matrix.os == 'linux'
     - run: brew install fish