Bump docker/build-push-action from 2 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 2 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v2...v6)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/docker-build.yml

@@ -21,7 +21,7 @@ jobs:
           username: ${{ github.repository_owner }}
           password: ${{ secrets.GHCR_PAT }}
       - name: Build Docker Image
-        uses: docker/build-push-action@v2
+        uses: docker/build-push-action@v6
         with:
           push: true
           tags: ghcr.io/${{ github.repository_owner }}/gh-act