[CI][bugfix]: Improve Qwen Image accuracy test with diffusers' RMSNorm (#4143)

Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Signed-off-by: Zeyu Huang | 黃澤宇 <11222265+fhfuih@users.noreply.github.com>
Signed-off-by: Gao Han <hgaoaf@connect.ust.hk>
Co-authored-by: Gao Han <hgaoaf@connect.ust.hk>

tests/e2e/accuracy/test_diffusers_backend_similarity.py

@@ -218,7 +218,7 @@ def _run_diffusers_qwen_image(*, model: str, output_path: Path) -> tuple[Image.I
             torch_dtype=torch.bfloat16,
             trust_remote_code=True,
         ).to("cuda")
-
+        pipe.transformer.set_attention_backend("_flash_3_hub")
         _diffusers_dummy_run(pipe)
 
         generator = torch.Generator(device="cuda").manual_seed(SEED)