chore(deps): update docker/build-push-action action to v6 (#88)

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This PR contains the following updates:

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

---

### Release Notes

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

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

[Compare
Source](https://togithub.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

---

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.github/workflows/nix.yml

@@ -58,7 +58,7 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USER }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
       - name: Build and Push Container
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           tags: matterlabsrobot/vault-auth-tee:latest
           push: ${{ github.event_name == 'push' ||  github.event_name == 'schedule' }}