[Test] Mock health callback in prefill abort cleanup fixture

[Fridge003]

Motivation

Follow-up to #36507, based on xinyuan/glm-5.3-flash-support.

CPU job 101456298849 fails all seven prefill-abort cleanup tests with AttributeError: '_Scheduler' object has no attribute 'maybe_send_health_check_signal'.

The tests introduced on main by #36988 instantiate only SchedulerDisaggregationPrefillMixin. The GLM branch calls the real scheduler's health-check callback after processing a prefill result, so this test double needs that collaborator too.

Modifications

Add self.maybe_send_health_check_signal = Mock() to the test-only _Scheduler fixture. One line, one test file; no production changes, assertion changes, or registration changes.

Validation

• Unpatched GLM-5.3-Flash support #36507 head 87de7ca9ba507093a276826aa83d52887793a4f8: all seven tests reproduce the missing-method failure.
• Patched source: all seven tests pass on an isolated CPU-only source copy on baizhou-nda, with all GPUs hidden.
• Command: CUDA_VISIBLE_DEVICES=8 PYTHONPATH=python python3 test/registered/unit/disaggregation/test_prefill_abort_result_cleanup.py -f.
• Targeted pre-commit and git diff --check pass.
• Single-file CPU /rerun-test: run 34023683974 passed, testing commit b7805652b9b633c0c54661b9918d0004e7dd6ca2 on ubuntu-latest. All seven tests passed; CPU job completed in 1m19s. No full CI requested.

Accuracy Tests

Not applicable: test-fixture-only change; all abort cleanup assertions are retained.

Speed Tests and Profiling

Not applicable: no runtime changes.

Checklist

• Formatting and applicable pre-commit checks pass.
• Existing regression tests reproduced before the fix and pass afterward.
• No documentation or performance updates required for this fixture-only fix.
• Existing test style and registration preserved.

[Fridge003]

/rerun-test test/registered/unit/disaggregation/test_prefill_abort_result_cleanup.py

[github-actions]

Results for /rerun-test test/registered/unit/disaggregation/test_prefill_abort_result_cleanup.py:

🚀 ubuntu-latest (1 test): ✅ View workflow run

cd test/ && python3 registered/unit/disaggregation/test_prefill_abort_result_cleanup.py