Bump actions/checkout from 4 to 6 (#5015)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/labled_test_310.yaml

@@ -77,7 +77,7 @@ jobs:
           apt install git -y
 
       - name: Checkout vllm-project/vllm-ascend repo
-        uses: actions/checkout@v6.0.1
+        uses: actions/checkout@v6
 
       - name: Install system dependencies
         run: |
@@ -85,7 +85,7 @@ jobs:
           apt-get -y install git vim wget net-tools gcc g++ cmake libnuma-dev curl gnupg2
 
       - name: Checkout vllm-project/vllm repo
-        uses: actions/checkout@v6.0.1
+        uses: actions/checkout@v6
         with:
           repository: vllm-project/vllm
           ref: ${{ matrix.vllm_version }}