tests: xfail attention sink UT for sliding window + non causal case (#1752)

Author: yzh119

tests/test_attention_sink.py

@@ -635,6 +635,11 @@ def test_attention_sink_chunk_prefill(
     Simulate chunk-based processing of long sequences where current chunk
     attends to all historical tokens plus current chunk tokens
     """
+    if not causal and window_left >= 0:
+        # xfail for non-causal + sliding window case
+        pytest.xfail(
+            "NOTE(Zihao): attention sink with sliding window and non-causal will fail after https://github.com/flashinfer-ai/flashinfer/pull/1661, temporarily xfail the test."
+        )
     torch.manual_seed(42)
     device = torch.device("cuda:0")
     if backend == "fa3" and not is_sm90a_supported(device):