[bugfix]Intermittent CI failure in the triton runtime jit (#5733)

### What this PR does / why we need it?
fix bug : https://github.com/vllm-project/vllm-ascend/issues/5634
Intermittent CI failure due to a compilation error in the triton
operator
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef

---------

Signed-off-by: Meihan-chen <jcccx.cmh@gmail.com>

.github/workflows/_unit_test.yaml

@@ -62,6 +62,9 @@ jobs:
       - name: Install Ascend toolkit & triton_ascend
         shell: bash -l {0}
         run: |
+          apt-get -y install clang-15
+          update-alternatives --install /usr/bin/clang clang /usr/bin/clang-15 20
+          update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-15 20
           BISHENG_NAME="Ascend-BiSheng-toolkit_aarch64_20260105.run"
           BISHENG_URL="https://vllm-ascend.obs.cn-north-4.myhuaweicloud.com/vllm-ascend/${BISHENG_NAME}"
           wget -O "${BISHENG_NAME}" "${BISHENG_URL}" && chmod a+x "${BISHENG_NAME}" && "./${BISHENG_NAME}" --install && rm "${BISHENG_NAME}"