add CI workflow (#989)

This will run the build script as a minimum to make sure that the build
script itself works. This doesn't verify the output yet.

However, this should prevent version bumps in packages with a different
API to be (auto) merged.

.github/workflows/CI.yml

@@ -0,0 +1,42 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: read
+
+env:
+  CI: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [18]
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+          registry-url: 'https://registry.npmjs.org'
+
+      - name: Use cached node_modules
+        uses: actions/cache@v3
+        with:
+          path: node_modules
+          key: ${{ runner.os }}-${{ matrix.node-version }}-node_modules-${{ hashFiles('**/package-lock.json') }}
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Build
+        run: npm run build