Update checkout action URL to use Gitea's repository

.gitea/workflows/demo.yaml

@@ -10,7 +10,7 @@ jobs:
       - run: echo "🐧 This job is now running on a ${{ runner.os }} server hosted by Gitea!"
       - run: echo "🔎 The name of your branch is ${{ gitea.ref }} and your repository is ${{ gitea.repository }}."
       - name: Check out repository code
-        uses: actions/checkout@v4
+        uses: https://gitea.com/actions/checkout@v4
       - run: echo "💡 The ${{ gitea.repository }} repository has been cloned to the runner."
       - run: echo "🖥️ The workflow is now ready to test your code on the runner."
       - name: List files in the repository