[CI]Fix nightly clang installation following previous attempt (#5907)

### What this PR does / why we need it?
This PR fixes the issue where the previous PR
https://github.com/vllm-project/vllm-ascend/pull/5733 failed to install
Clang in nightly environment.

- vLLM version: v0.13.0
- vLLM main:
bde38c11df

---------

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

tests/e2e/nightly/multi_node/scripts/run.sh

@@ -127,7 +127,7 @@ install_extra_components() {
 
 install_triton_ascend() {
     echo "====> Installing triton_ascend"
-    apt-get install -y clang-15
+    apt-get update && apt-get install -y 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
     clang -v