change to gitea checkout

.gitea/workflows/demo.yaml

@@ -7,8 +7,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout code
-        uses: actions/checkout@v2
+      - checkout: {}
       
       - name: Build Docker image
         run: docker build -t my-image:latest .