fix timezone failures

[msaroufim]

followup work from fbed4bb since tests weren't updated

AMD timeout feels like a flake

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[Copilot]

Pull request overview

This PR fixes timezone-related test failures by making datetime objects timezone-aware in test mock data. The changes align the test fixtures with the actual implementation in submission.py, which uses UTC timezone-aware datetime for deadline comparisons.

Key Changes

• Updated mock deadline values to use datetime.datetime.now(datetime.timezone.utc) instead of naive datetime.datetime.now()
• Applied consistently across all three occurrences in the test file (mock fixture and two test cases)

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