Update alpine Docker tag to v3.21.0

This MR contains the following updates:

Package	Type	Update	Change
alpine	final	minor	3.20.3 -> 3.21.0

---

⚠️ Warning

Some dependencies could not be looked up. Check the Dependency Dashboard for more information.

---

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 MR becomes conflicted, or you tick the rebase/retry checkbox.

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

---

• If you want to rebase/retry this MR, check this box

---

This MR has been generated by Renovate Bot.