⬆️ Update docker/build-push-action action to v6 (#53)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [docker/build-push-action](https://github.com/docker/build-push-action) | action | major | `v5` -> `v6` |

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### Release Notes

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

### [`v6`](https://github.com/docker/build-push-action/compare/v5...v6)

[Compare Source](https://github.com/docker/build-push-action/compare/v5...v6)

</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:eyJjcmVhdGVkSW5WZXIiOiIzNy40MTAuMiIsInVwZGF0ZWRJblZlciI6IjM3LjQxMC4yIiwidGFyZ2V0QnJhbmNoIjoibWFzdGVyIiwibGFiZWxzIjpbXX0=-->

Reviewed-on: #53
Co-authored-by: Renovate <renovate@sebclem.fr>
Co-committed-by: Renovate <renovate@sebclem.fr>

.gitea/workflows/docker.yml

@@ -40,7 +40,7 @@ jobs:
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: ${{ github.ref_type == 'tag' }}