ci: add tests and dependabot configs

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+  - package-ecosystem: npm
+    directory: "/"
+    schedule:
+      interval: daily
+    open-pull-requests-limit: 10
+    versioning-strategy: increase
+    ignore:
+      - dependency-name: "@types/node"
+        versions:
+          - ">=21"

.github/workflows/tests.yml

@@ -0,0 +1,20 @@
+name: tests
+on: [push, pull_request]
+jobs:
+  tests:
+    name: node ${{ matrix.node-version }} / ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version: [20]
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: npm
+      - run: npm ci
+      - run: npm test