build(deps): bump cachix/install-nix-action in /.github/workflows

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/nix.yml

@@ -22,7 +22,7 @@ jobs:
         runs-on: ubuntu-latest
         steps:
             - uses: actions/checkout@v4
-            - uses: cachix/install-nix-action@V27
+            - uses: cachix/install-nix-action@V28
               with:
                   nix_path: nixpkgs=channel:nixos-unstable
             - uses: DeterminateSystems/magic-nix-cache-action@v8