ci: use Gitea mirror instead of GitHub

.gitea/workflows/build-demo.yaml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout master
-        uses: actions/checkout@v4
+        uses: https://gitea.com/actions/checkout@v4
 
       - name: Install Python
         run: sudo apt-get install python3.9
@@ -15,7 +15,7 @@ jobs:
         run: pip install mkdocs-material
 
       - name: Setup Node.js
-        uses: actions/setup-node@v4
+        uses: https://gitea.com/actions/setup-node@v4
         with:
           node-version: '20'
 
@@ -26,7 +26,7 @@ jobs:
         run: npm run build
 
       - name: Upload Output
-        uses: actions/upload-artifact@v4
+        uses: https://gitea.com/actions/upload-artifact@v4
         with:
           name: static-website
           path: site/