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](https://github.com/cachix/install-nix-action/compare/V27...V28)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/update.yaml

@@ -10,7 +10,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@V27
+        uses: cachix/install-nix-action@V28
         with:
           nix_path: nixpkgs=channel:nixos-unstable
           extra_nix_config: |