gh-158097: Make test_staggered_race_with_eager_tasks deterministic

Lib/test/test_asyncio/test_eager_task_factory.py

@@ -217,7 +217,12 @@ def test_staggered_race_with_eager_tasks(self):
         # See https://github.com/python/cpython/issues/124309
 
         async def fail():
-            await asyncio.sleep(0)
+            # Fail without suspending first.  staggered_race() awaits the
+            # coroutines inline and cancels every one of them that has not
+            # finished once another one wins, so a coroutine that yields before
+            # raising may be cancelled instead, and excs[2] would report a
+            # CancelledError.  Raising right away keeps the outcome
+            # independent of how busy the event loop is.
             raise ValueError("no good")
 
         async def blocked():

Misc/NEWS.d/next/Tests/2026-09-30-00-00-00.gh-issue-158097.pcB3mO.rst

@@ -0,0 +1,2 @@
+Fix a rare flakiness in ``test_staggered_race_with_eager_tasks`` in
+``test_asyncio``.