Bump cachix/install-nix-action from v11 to v12 (#11)

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from v11 to v12.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](https://github.com/cachix/install-nix-action/compare/v11...07da2520eebede906fbeefa9dd0a2b635323909d)

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@v11
+      - uses: cachix/install-nix-action@v12
         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