Update nixpkgs digest to d4c28e7

[SuperSandroBot]

This PR contains the following updates:

Package	Update	Change
nixpkgs	digest	bc947f5 -> d4c28e7

---

Configuration

📅 Schedule: Branch creation - "before 12am on sunday" (UTC), 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 Renovate Bot.