Update GitHub Actions runner to depot-ubuntu-24.04

[janavenkat]

Summary

Migrate all GitHub Actions workflow runners from ubuntu-latest to depot-ubuntu-24.04 in both ci.yml (linter + pytest jobs) and build.yml (build + publish jobs).

Review & Testing Checklist for Human

• Verify that depot-ubuntu-24.04 runners are available and configured for this repository (if Depot isn't set up, all workflows will fail)
• After merging, confirm CI passes on the next push — especially the Python matrix tests (3.9–3.12) and the PyPI publish job, since Ubuntu 24.04 may ship different system-level dependencies

[devin-ai-integration]

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