Fix bump-upstream job by correcting Portainer upstream release source

[Copilot]

The bump-upstream GitHub Actions job was failing because upstream version discovery queried a non-existent releases endpoint (portainer/portainer-ce), returning 404. This PR updates the upstream source to the repository that actually publishes Portainer releases.

• Root cause

  • bump-upstream calls GitHub Releases for the configured upstream repo.
  • Current config pointed to portainer/portainer-ce, which does not expose releases via that endpoint.

• Config update

  • Updated package upstream metadata in dappnode_package.json:
    • repo: "portainer/portainer-ce" → repo: "portainer/portainer"

• Impact

  • Restores upstream tag resolution for the automation used by the bump-upstream workflow.

"upstream": [
  {
    "repo": "portainer/portainer",
    "version": "v2.27.7",
    "arg": "UPSTREAM_VERSION_PORTAINER"
  }
]