[Core][aDAG] Set buffer size to 1 for regression (#47639)

There's a regression with buffer size 10. I am going to investigate but I will revert it to buffer size 1 for now until further investigation.
With buffer size 1, regression seems to be gone https://buildkite.com/ray-project/release/builds/22594#0191ed4b-5477-45ff-be9e-6e098b5fbb3c. probably some sort of contention or sth like that

python/ray/dag/compiled_dag_node.py

@@ -611,7 +611,7 @@ def __init__(
             # We conservatively set num_shm_buffers to _max_inflight_executions.
             # It means that the DAG can be underutilized, but it guarantees there's
             # no false positive timeouts.
-            num_shm_buffers=self._max_inflight_executions,
+            num_shm_buffers=1,
         )
         if not isinstance(self._buffer_size_bytes, int) or self._buffer_size_bytes <= 0:
             raise ValueError(

python/ray/dag/tests/experimental/test_accelerated_dag.py

@@ -2122,6 +2122,7 @@ def test_driver_and_actor_as_readers(ray_start_cluster):
         dag.experimental_compile()
 
 
+@pytest.mark.skip("Currently buffer size is set to 1 because of regression.")
 @pytest.mark.parametrize("temporary_change_timeout", [1], indirect=True)
 def test_buffered_inputs(shutdown_only, temporary_change_timeout):
     ray.init()