test: Add Node 20 to CI matrix (#41)

.github/workflows/ci.yml

@@ -6,6 +6,11 @@ on:
 jobs:
   tests:
     runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        node: [18, 20]
+    continue-on-error: ${{ matrix.node == 20 }}
+
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -16,7 +21,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version-file: '.nvmrc'
+          node-version: ${{ matrix.node }}
 
       - name: Install dependencies
         run: npm ci