Seed sgl-kernel topk sigmoid tests on all backends (#30754)

sgl-kernel/tests/test_moe_topk_sigmoid.py

@@ -5,18 +5,14 @@ import pytest
 import torch
 from sgl_kernel import topk_sigmoid
 
-_IS_HIP = torch.version.hip is not None
-
 
 @pytest.fixture(autouse=True)
 def _deterministic_seed():
-    # AMD/ROCm only: pin RNG so torch.randn produces identical gating scores
+    # Pin RNG on every backend so torch.randn produces identical gating scores
-    # across runs. atol=0 indices comparison is otherwise tripped by near-tied
+    # across runs. The exact index comparison can otherwise be tripped by
-    # sigmoid scores where hipCUB's tie-break inside torch.topk disagrees with
+    # near-tied sigmoid scores whose rounded values have different top-k
-    # sgl_kernel.topk_sigmoid. Not observed on CUDA, so leave CUDA behavior
+    # tie-break ordering between torch.topk and sgl_kernel.topk_sigmoid.
-    # unchanged.
+    torch.manual_seed(0)
-    if _IS_HIP:
-        torch.manual_seed(0)
 
 
 @pytest.mark.parametrize(