[CI]Nightly test use main (#6502)

### What this PR does / why we need it?
Nightly test use `main`

- vLLM version: v0.15.0
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.15.0

Signed-off-by: MrZ20 <2609716663@qq.com>

.github/workflows/schedule_nightly_image_build.yaml

@@ -22,9 +22,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
-        with:
-          fetch-depth: 0
-          ref: releases/v0.13.0
 
       - name: Show build target
         run: |