fix vllm version

Signed-off-by: MengqingCao <cmq0113@163.com>

Author: MengqingCao

.github/workflows/vllm_ascend_test.yaml

@@ -107,11 +107,9 @@ jobs:
         run: |
           apt-get -y install `cat packages.txt`
 
-      - name: Checkout vllm-project/vllm repo
-        uses: actions/checkout@v4
-        with:
-          repository: vllm-project/vllm
-          path: ./vllm-empty
+      - name: Clone vllm-project/vllm repo
+        run: |
+          git clone --depth 1 --branch v0.7.3 https://github.com/vllm-project/vllm.git ./vllm-empty
 
       - name: Install vllm-project/vllm from source
         working-directory: ./vllm-empty