[CI/Build][AMD] Skip if flash_attn_varlen_func not available in test_aiter_flash_attn.py (#29043)

Signed-off-by: Randall Smith <ransmith@amd.com>
Co-authored-by: Randall Smith <ransmith@amd.com>

tests/kernels/attention/test_aiter_flash_attn.py

@@ -6,6 +6,7 @@ import pytest
 import torch
 
 import vllm.v1.attention.backends.rocm_aiter_fa  # noqa: F401
+from vllm.attention.utils.fa_utils import is_flash_attn_varlen_func_available
 from vllm.platforms import current_platform
 
 NUM_HEADS = [(4, 4), (8, 2)]
@@ -100,6 +101,8 @@ def test_varlen_with_paged_kv(
     num_blocks: int,
     q_dtype: torch.dtype | None,
 ) -> None:
+    if not is_flash_attn_varlen_func_available():
+        pytest.skip("flash_attn_varlen_func required to run this test.")
     torch.set_default_device("cuda")
     current_platform.seed_everything(0)
     num_seqs = len(seq_lens)