chore: bump actions/download-artifact from 4 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/integration.yml

@@ -358,7 +358,7 @@ jobs:
           # the output should be in the .cr-release-packages since cr index expects to find it there to create the helm index
           helm package deployments/liqo --version "${{ needs.configure.outputs.commit-ref }}" --app-version "${{ needs.configure.outputs.commit-ref }}" --destination .cr-release-packages
 
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v6
         with:
           path: ./liqoctl/