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/schedule_test_benchmarks.yaml

@@ -95,12 +95,12 @@ jobs:
           git config --global url."https://gh-proxy.test.osinfra.cn/https://github.com/".insteadOf https://github.com/
 
       - name: Checkout vllm-project/vllm-ascend repo
-        uses: actions/checkout@v6.0.1
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
       - name: Checkout vllm-project/vllm repo
-        uses: actions/checkout@v6.0.1
+        uses: actions/checkout@v6
         with:
           repository: vllm-project/vllm
           path: ./vllm-empty