Bump cachix/cachix-action from 12 to 13 (#382)

Bumps [cachix/cachix-action](https://github.com/cachix/cachix-action) from 12 to 13.
- [Release notes](https://github.com/cachix/cachix-action/releases)
- [Commits](cachix/cachix-action@v12...v13)

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

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

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
       with:
         nix_path: 'nixpkgs=./nix'
     - name: "Install Cachix"
-      uses: cachix/cachix-action@v12
+      uses: cachix/cachix-action@v13
       with:
         name: niv
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'