Update cachix/cachix-action action to v13

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
cachix/cachix-action	action	major	v12 -> v13

---

Release Notes

cachix/cachix-action (cachix/cachix-action)

### [`v13`](https://togithub.com/cachix/cachix-action/releases/tag/v13): cachix-action-v13 [Compare Source](https://togithub.com/cachix/cachix-action/compare/v12...v13) - run on node20 - add `skipAddingSubstituter` to skip running `cachix use`

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Mend Renovate. View repository job log here.