Update alpine Docker tag to v3.15.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
alpine	final	minor	3.14.2 -> 3.15.0

---

Configuration

📅 Schedule: At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ 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, click this checkbox.

---

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