ci: fall back to Node 20.18.0 (setup-node supported)

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '22.9.0'
+          node-version: '20.18.0'
           cache: pnpm
           cache-dependency-path: pnpm-lock.yaml