ci: fix checkout action version format

Author: pwwang

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
         python-version: [3.9, "3.10", "3.11", "3.12"]
 
     steps:
-      - uses: actions/checkout@6
+      - uses: actions/checkout@v6
       - name: Install uv
         uses: astral-sh/setup-uv@v8.0.0
         with: