[Bugfix] Fix failing GPT-OSS initialization test (#22557)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>

tests/models/test_initialization.py

@@ -68,6 +68,11 @@ def can_initialize(model_arch: str, monkeypatch: pytest.MonkeyPatch,
         if model_arch == "Phi4FlashForCausalLM":
             # Phi4FlashForCausalLM only supports DIFFERENTIAL_FLASH_ATTN backend
             m.setenv("VLLM_ATTENTION_BACKEND", "DIFFERENTIAL_FLASH_ATTN")
+        if model_arch == "GptOssForCausalLM":
+            # FIXME: A hack to bypass FA3 assertion because our CI's L4 GPU
+            # has cc==8.9 which hasn't supported FA3 yet. Remove this hack when
+            # L4 supports FA3.
+            m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN_VLLM_V1")
         LLM(
             model_info.default,
             tokenizer=model_info.tokenizer,