Add initial Gitea Actions workflow

.gitea/workflows/demo.yaml

@@ -0,0 +1,13 @@
+name: Hello Gitea Actions
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run a one-line script
+        run: echo "Hello, Gitea Actions!"
+      - name: Run a multi-line script
+        run: |
+          echo Add other actions as you wish...
+          echo Such as building your code, running tests, or deploying.