Update docker/setup-buildx-action action to v4 (#176)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
|
[docker/setup-buildx-action](https://redirect.github.com/docker/setup-buildx-action)
| action | major | `v3` → `v4` |

---

### Release Notes

<details>
<summary>docker/setup-buildx-action
(docker/setup-buildx-action)</summary>

###
[`v4`](https://redirect.github.com/docker/setup-buildx-action/compare/v3...v4)

[Compare
Source](https://redirect.github.com/docker/setup-buildx-action/compare/v3...v4)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
Automerge - At any time (no schedule defined).

🚦 **Automerge**: Enabled.

♻ **Rebasing**: Whenever PR is behind base branch, 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 was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/platform-mesh/resource-broker).

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Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -66,7 +66,7 @@ jobs:
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
       - uses: docker/setup-qemu-action@ce360397dd3f832beb865e1373c09c0e9f86d70a # v4
-      - uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3
+      - uses: docker/setup-buildx-action@4d04d5d9486b7bd6fa91e7baf45bbb4f8b9deedd # v4
 
       - uses: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2 # v4
         with: