Fix flaky test_adjust_maintenance_mode_based_on_sysinfo_exit

[FrankYang0529]

Why

• EdgeWorker.maintenance_mode / maintenance_comments are class attributes. The test_heartbeat set EdgeWorker.maintenance_mode = True on class level and doesn't cleanup.
• CI runs provider unit tests with pytest -n auto, so test order is dynamic.
• If test_heartbeat runs right before test_adjust_maintenance_mode_based_on_sysinfo_exit, the leaked True makes test_adjust_maintenance_mode_based_on_sysinfo_exit fail.

How

• Add an autouse reset_maintenance_state fixture to TestEdgeWorker that resets EdgeWorker.maintenance_mode / EdgeWorker.maintenance_comments before each test, and after it.

Sample Failed Run

• https://github.com/apache/airflow/actions/runs/29023005614/job/86140259202
• https://github.com/apache/airflow/actions/runs/29070727959/job/86293011141

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Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

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