ci: bump nodejs to v20

Author: foosel

.github/workflows/docs.yaml

@@ -77,7 +77,7 @@ jobs:
         if: github.event_name == 'push' || github.event_name == 'workflow_dispatch' || github.event.client_payload.ref == format('refs/{0}/{1}', matrix.source, matrix.version)
         uses: actions/setup-node@v3
         with:
-          node-version: "16"
+          node-version: "20"
 
       - name: 🏗 Install mermaid-cli
         if: github.event_name == 'push' || github.event_name == 'workflow_dispatch' || github.event.client_payload.ref == format('refs/{0}/{1}', matrix.source, matrix.version)