Gate publish workflow to upstream org only

[Copilot]

This change restricts chart publishing to repositories owned by PelicanPlatform, preventing publish execution in forks while preserving upstream trigger behavior.

• Scope

  • Updated .github/workflows/publish.yaml only.
  • No trigger/event changes; existing push behavior remains intact for upstream repos.

• Workflow guard

  • Added a job-level organization check on publish:
    • if: github.repository_owner == 'PelicanPlatform'
  • Result:
    • Upstream (PelicanPlatform/*): job runs as before.
    • Forks (other owners): job is skipped, so no publish step executes.

• Applied change

  jobs:
    publish:
      name: Package & Push
      if: github.repository_owner == 'PelicanPlatform'
      runs-on: ubuntu-latest

[matyasselmeci]

Does what it says on the can

[matyasselmeci]

(the workflow is disabled on this repo anyway, but that doesn't get inherited by forks, where it just runs and fails)