chore(deps): update woodpeckerci/plugin-docker-buildx docker tag to v4 (#8)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [woodpeckerci/plugin-docker-buildx](https://codeberg.org/woodpecker-plugins/docker-buildx) ([source](https://codeberg.org/woodpecker-plugins/docker-buildx.git)) | major | `3.2.1` -> `4.0.0` |

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### Release Notes

<details>
<summary>woodpecker-plugins/docker-buildx (woodpeckerci/plugin-docker-buildx)</summary>

### [`v4.0.0`](https://codeberg.org/woodpecker-plugins/docker-buildx/releases/tag/v4.0.0)

[Compare Source](https://codeberg.org/woodpecker-plugins/docker-buildx/compare/v3.2.1...v4.0.0)

-   chore(deps): update docker docker tag to v26.1.0
-   chore(deps): update docker/buildx-bin docker tag to v0.14.0 ([#&#8203;155](https://github.com/woodpecker-plugins/docker-buildx/issues/155))

</details>

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### Configuration

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Reviewed-on: #8
Co-authored-by: renovate-bot <renovate@ocram85.com>
Co-committed-by: renovate-bot <renovate@ocram85.com>

.woodpecker/ci.yml

@@ -5,7 +5,7 @@ when:
       - ${CI_REPO_DEFAULT_BRANCH}
 
 variables:
-  - &build_plugin 'woodpeckerci/plugin-docker-buildx:3.2.1'
+  - &build_plugin 'woodpeckerci/plugin-docker-buildx:4.0.0'
   # deployment targets
   # TODO: Disabled docker hub target until first release is ready / Rate Limits
   - &publish_repos 'ocram85/plugin-gitea-package,gitea.ocram85.com/plugins/gitea-package'