upgrade actions/setup-node from v2 -> v4 (actions/setup-node#1275 (comment))

Author: huan

.github/workflows/gh-pages.yml

@@ -19,7 +19,7 @@ jobs:
         run: |
           sudo gem install bundler
 
-      - uses: actions/setup-node@v2
+      - uses: actions/setup-node@v4
         with:
           node-version: 20
           cache: 'npm'
@@ -53,7 +53,7 @@ jobs:
         sudo gem install bundler
         # bundle config path ~/.npm/bundle
 
-    - uses: actions/setup-node@v2
+    - uses: actions/setup-node@v4
       with:
         node-version: 18
         cache: 'npm'