Update alpine Docker tag to v3.21.2 (petejohanson#8)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| alpine | patch | `3.21.1` -> `3.21.2` |

---

### 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.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOS45My4wIiwidXBkYXRlZEluVmVyIjoiMzkuOTMuMCIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOltdfQ==-->

Reviewed-on: https://git.chdorner.com/chdorner/panic34/pulls/8
Co-authored-by: Renovate Bot <[email protected]>
Co-committed-by: Renovate Bot <[email protected]>

.woodpecker/build.yml

@@ -20,7 +20,7 @@ steps:
       # - west build -s zmk/app -b seeeduino_xiao_ble -d build/zaphod_lite_xiao_ble -- -DZMK_CONFIG="$CI_WORKSPACE/config" -DSHIELD=zaphod_lite
       - cat -n build/zaphod/zephyr/.config
   - name: upload
-    image: alpine:3.21.1@sha256:b97e2a89d0b9e4011bb88c02ddf01c544b8c781acf1f4d559e7c8f12f1047ac3
+    image: alpine:3.21.2@sha256:56fa17d2a7e7f168a043a2712e63aed1f8543aeafdcee47c58dcffe38ed51099
     commands:
       - apk add curl
       - stat build/zaphod/zephyr/zmk.uf2