fix: use fa3 unit test on hopper only (#5304)

sgl-kernel/tests/test_flash_attention.py

@@ -17,7 +17,7 @@ def is_fa3_supported(device=None) -> bool:
     #  https://docs.nvidia.com/cuda/cuda-c-programming-guide/#shared-memory-8-x
     #  now sgl-kernel only build fa3 for sm90a && cuda >= 12.4
     return (
-        (torch.cuda.get_device_capability(device)[0] >= 9)
+        (torch.cuda.get_device_capability(device)[0] == 9)
         and (torch.version.cuda >= "12.4")
         # or torch.cuda.get_device_capability(device) == (8, 0)
         # or torch.cuda.get_device_capability(device) == (8, 7)