Bump cachix/cachix-action from 15 to 16 (#1018)

Bumps [cachix/cachix-action](https://github.com/cachix/cachix-action) from 15 to 16.
- [Release notes](https://github.com/cachix/cachix-action/releases)
- [Commits](https://github.com/cachix/cachix-action/compare/v15...v16)

---
updated-dependencies:
- dependency-name: cachix/cachix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/ci.yml

@@ -40,7 +40,7 @@ jobs:
         if: ${{ matrix.os != 'windows-latest' }}
         with:
           nix_path: nixpkgs=channel:nixos-unstable
-      - uses: cachix/cachix-action@v15
+      - uses: cachix/cachix-action@v16
         if: ${{ matrix.os != 'windows-latest' && env.CACHIX_AUTH_TOKEN != '' }}
         with:
           authToken: ${{ env.CACHIX_AUTH_TOKEN }}