chore(deps): update actions/build-push-action action to v6 (#22)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/build-push-action](https://gitea.ocram85.com/actions/build-push-action) | action | major | `v4` -> `v6` |

---

### Release Notes

<details>
<summary>actions/build-push-action (actions/build-push-action)</summary>

### [`v6`](https://gitea.ocram85.com/actions/build-push-action/compare/v5...v6)

[Compare Source](https://gitea.ocram85.com/actions/build-push-action/compare/v5...v6)

### [`v5`](https://gitea.ocram85.com/actions/build-push-action/compare/v4...v5)

[Compare Source](https://gitea.ocram85.com/actions/build-push-action/compare/v4...v5)

</details>

---

### 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:eyJjcmVhdGVkSW5WZXIiOiIzNy40MTMuMiIsInVwZGF0ZWRJblZlciI6IjM3LjQxMy4yIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJyZW5vdmF0ZSJdfQ==-->

Reviewed-on: #22
Reviewed-by: OCram85 <marco.blessing@googlemail.com>
Co-authored-by: renovate-bot <renovate@ocram85.com>
Co-committed-by: renovate-bot <renovate@ocram85.com>

.gitea/workflows/ci.yaml

@@ -42,7 +42,7 @@ jobs:
           password: ${{ secrets.TOKEN }}
       -
         name: Build and push
-        uses: https://gitea.ocram85.com/actions/build-push-action@v4
+        uses: https://gitea.ocram85.com/actions/build-push-action@v6
         with:
           push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}