Bump cachix/install-nix-action from v12 to v13 (#25)

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/nix.yml

@@ -9,7 +9,7 @@ jobs:
         with:
           # Nix Flakes doesn't work on shallow clones
           fetch-depth: 0
-      - uses: cachix/install-nix-action@v12
+      - uses: cachix/install-nix-action@v13
         with:
           install_url: https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20200618_377345e/install
       - run: echo "experimental-features = nix-command flakes" | sudo tee -a /etc/nix/nix.conf