build(deps): bump cachix/install-nix-action from V27 to 28

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from V27 to 28. This release includes the previously tagged commit.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@V27...V28)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/build-nix.yml

@@ -29,7 +29,7 @@ jobs:
         make-step: ['nix-build', 'nix-build-cmake-qt5']
     steps:
       - name: ⚙️ Install Nix
-        uses: cachix/install-nix-action@V27
+        uses: cachix/install-nix-action@V28
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - name: 🧰 Checkout code