Enabling some B200-specific tests on MI355 (#35253)

Signed-off-by: Alexei V. Ivanov <alexei.ivanov@amd.com>
Signed-off-by: Alexei-V-Ivanov-AMD <156011006+Alexei-V-Ivanov-AMD@users.noreply.github.com>

tests/kernels/attention/test_attention_selector.py

@@ -343,6 +343,10 @@ def test_auto_backend_selection_behavior():
         ("FLEX_ATTENTION", None, False),  # Flex does not support
     ],
 )
+@pytest.mark.skipif(
+    current_platform.is_rocm(),
+    reason="Attention backend FA3 is not supported on ROCm. This test can't succeed.",
+)
 def test_per_head_quant_scales_backend_selection(
     backend_name: str, flash_attn_version: int | None, should_succeed: bool
 ):