[CI] Pull latest vllm-ascend src before tests (#4988)

### What this PR does / why we need it?
Currently, our image build suffers from errors during cross-compilation,
which causing the image to fail to build sometimes(see
https://github.com/vllm-project/vllm-ascend/actions/runs/20152861650/job/57849208186).
This results in the nightly test code not being the latest version.

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: wangli <wangli858794774@gmail.com>

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

@@ -124,6 +124,16 @@ kill_npu_processes() {
   sleep 4
 }
 
+upgrade_vllm_ascend_scr() {
+    # Fix me(Potabk): Remove this once our image build use 
+    # The separate architecture build process currently suffers from errors during cross-compilation
+    # causing the image to fail to build correctly. 
+    # This results in the nightly test code not being the latest version.
+    cd "$WORKSPACE/vllm-ascend"
+    git pull origin main
+    
+}
+
 run_tests_with_log() {
     set +e
     kill_npu_processes
@@ -146,6 +156,7 @@ main() {
     if [[ "$CONFIG_YAML_PATH" == *"DeepSeek-V3_2-Exp-bf16.yaml" ]]; then
         install_extra_components
     fi
+    upgrade_vllm_ascend_scr
     cd "$WORKSPACE/vllm-ascend"
     run_tests_with_log
 }