Update actions/checkout action to v4 (#357)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/forum_update.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: 签出代码
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: 初始化Python
       uses: actions/setup-python@v5