Bump cachix/install-nix-action from V27 to 30

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from V27 to 30. 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...v30)

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

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

.github/workflows/test.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4.1.7
-      - uses: cachix/install-nix-action@V27
+      - uses: cachix/install-nix-action@v30
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - run: nix flake check

.github/workflows/update.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4.1.7
-      - uses: cachix/install-nix-action@V27
+      - uses: cachix/install-nix-action@v30
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - run: ./update