ci: bump cachix/install-nix-action from v12 to v13 (#10)

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](https://github.com/cachix/install-nix-action/compare/v12...8d6d5e949675fbadb765c6b1a975047fa5f09b27)

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

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

.github/workflows/build.yml

@@ -38,7 +38,7 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v2.3.4
     - name: Install nix
-      uses: cachix/install-nix-action@v12
+      uses: cachix/install-nix-action@v13
       with:
         nix_path: "${{ matrix.nixPath }}"
     - name: Show nixpkgs version