Add dependabot config, update ci workflow

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [14.x, 16.x, 18.x]
+        node: [18.x, 20.x, 21.x]
     steps:
       - name: Checkout code
         uses: actions/checkout@v3
@@ -52,7 +52,7 @@ jobs:
         id: pnpm-install
         uses: pnpm/action-setup@v2
         with:
-          version: 7
+          version: 8
           run_install: false
 
       - name: Get pnpm store directory