[V1] reduce block size for tree attention correctness test to fix 'ou… (vllm-project#22207)

Signed-off-by: Giancarlo Delfin <gdelfin@meta.com>
Signed-off-by: Xiao Yu <xiao.yu@amd.com>

Author: TheEpicDolphin

tests/v1/spec_decode/test_tree_attention.py

@@ -155,7 +155,7 @@ def test_tree_attn_correctness() -> None:
 
     dim_per_head = 128
     num_kv_heads = 2
-    block_size = 128
+    block_size = 32
     max_sequence_length = 8192
     randomize_blocks = True
     for batch_size in [1, 16, 32]: