Update CI artifact actions to restore crosstool (ubuntu-latest) workflow execution

[Copilot]

The crosstool (ubuntu-latest) job was failing during workflow setup, before any build logic ran. The failure came from deprecated actions/upload-artifact@v2 / actions/download-artifact@v2 usage in the CI workflow.

• Root cause

  • GitHub Actions now rejects the deprecated v2 artifact actions, causing the crosstool job to fail at action resolution time.

• Workflow updates

  • Upgraded all artifact steps in .github/workflows/continuous-integration-workflow.yml:
    • actions/upload-artifact@v2 → actions/upload-artifact@v4
    • actions/download-artifact@v2 → actions/download-artifact@v4

• Artifact compatibility

  • Set the download destination explicitly to preserve the existing handoff between jobs, so ct-ng.tar remains available where the extraction step expects it.

- name: "download ct-ng"
  uses: actions/download-artifact@v4
  with:
    name: crosstool.${{ matrix.host }}
    path: .

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• dl.google.com
  • Triggering command: /usr/lib/apt/methods/https /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)