build(deps): bump cachix/install-nix-action from 23 to 28

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 23 to 28.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v23...V28)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/nixpkgs.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v23
+      - uses: cachix/install-nix-action@V28
         with:
           install_url: https://releases.nixos.org/nix/nix-${{ env.NIX_VERSION }}/install
       - run: make nixpkgs

.github/workflows/test.yml

@@ -120,7 +120,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v23
+      - uses: cachix/install-nix-action@V28
         with:
           install_url: https://releases.nixos.org/nix/nix-${{ env.NIX_VERSION }}/install
       - uses: cachix/cachix-action@v12
@@ -142,7 +142,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v23
+      - uses: cachix/install-nix-action@V28
         with:
           install_url: https://releases.nixos.org/nix/nix-${{ env.NIX_VERSION }}/install
       - uses: cachix/cachix-action@v12
@@ -164,7 +164,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v23
+      - uses: cachix/install-nix-action@V28
         with:
           install_url: https://releases.nixos.org/nix/nix-${{ env.NIX_VERSION }}/install
       - uses: cachix/cachix-action@v12