get something working with GitHub actions for CI.

.github/workflows/ci.yml

@@ -0,0 +1,16 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '18'
+          cache: 'npm'
+      - run: npm test
+