test(proxy): pin that the scheduler stops before the shutdown drain flushes

Nothing asserted the ordering between stopping the scheduler and flushing, so
moving the stop after the flush loop still passed while letting a scheduled job
race the final drain.

tests/test_litellm/proxy/proxy_server/test_lifecycle.py

@@ -865,3 +865,25 @@ async def test_drain_spend_buffers_propagates_cancellation(monkeypatch):
         await ps._drain_spend_buffers_on_shutdown()
 
     assert deps.tag_spend.await_count == 0
+
+
+@pytest.mark.asyncio
+async def test_drain_spend_buffers_stops_scheduler_before_flushing(monkeypatch):
+    order: List[str] = []
+
+    scheduler = MagicMock()
+    scheduler.shutdown.side_effect = lambda **kwargs: order.append("scheduler_stopped")
+
+    async def _flush(*args, **kwargs):
+        order.append("flush")
+
+    _patch_drain_deps(
+        monkeypatch,
+        scheduler=scheduler,
+        update_spend=AsyncMock(side_effect=_flush),
+        update_daily_tag_spend=AsyncMock(side_effect=_flush),
+    )
+
+    await ps._drain_spend_buffers_on_shutdown()
+
+    assert order == ["scheduler_stopped", "flush", "flush"]