Bump cachix/install-nix-action from v12 to v13 (#36)

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from v12 to v13.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v12...8d6d5e9)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/test.yml

@@ -7,5 +7,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: cachix/install-nix-action@v12
+    - uses: cachix/install-nix-action@v13
     - run: nix build -f . -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixpkgs-unstable.tar.gz