add forgejo actions ci workflow

.forgejo/workflows/ci.yml

@@ -0,0 +1,12 @@
+name: CI
+on: [push]
+jobs:
+  build:
+    runs-on: docker
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+      - run: node -e "console.log('Forgejo Actions works, node', process.version)"
+      - run: echo 'GH-Actions-syntax workflow ran unmodified on Forgejo'