ci: Dogfood nix from master for vm_tests and flake_regressions

This should provide more coverage for the build from master that
is being dogfooded.

(cherry picked from commit 3b3c02160d)

.github/workflows/ci.yml

@@ -182,7 +182,12 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: ./.github/actions/install-nix-action
+        with:
+          dogfood: true
+          extra_nix_config:
+            experimental-features = nix-command flakes
+          github_token: ${{ secrets.GITHUB_TOKEN }}
       - uses: DeterminateSystems/magic-nix-cache-action@main
       - run: |
           nix build -L \
@@ -208,6 +213,11 @@ jobs:
         with:
           repository: NixOS/flake-regressions-data
           path: flake-regressions/tests
-      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: ./.github/actions/install-nix-action
+        with:
+          dogfood: true
+          extra_nix_config:
+            experimental-features = nix-command flakes
+          github_token: ${{ secrets.GITHUB_TOKEN }}
       - uses: DeterminateSystems/magic-nix-cache-action@main
       - run: nix build -L --out-link ./new-nix && PATH=$(pwd)/new-nix/bin:$PATH MAX_FLAKES=25 flake-regressions/eval-all.sh