add checkout code

Author: RelativeSure

.github/workflows/files-changed.yml

@@ -44,6 +44,9 @@ jobs:
   update-readme:
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
       - name: Set up Python
         uses: actions/setup-python@v5
         with: