fix: Windows CI — relax runtime_ms assertion for low timer resolution

Windows has ~15ms timer resolution, so tasks that complete in <1ms
get runtime_ms=0.0. Changed assertion from > 0 to >= 0.

All 12 CI jobs should now pass (ubuntu/macos/windows × Python 3.10-3.13)

Author: bysiber

tests/test_worker.py

@@ -172,7 +172,7 @@ def result_task() -> dict:
         assert result is not None
         assert result.state == TaskState.SUCCESS
         assert result.result == {"status": "done", "count": 42}
-        assert result.runtime_ms > 0
+        assert result.runtime_ms >= 0  # Windows timer resolution can yield 0.0
 
     def test_worker_task_timeout(self, app, backend):
         @app.task(name="timeout_task", timeout=0.5, max_retries=0)