Updated the workflow to use Node.js 20

Author: brown9804

.github/workflows/validate_and_fix_markdown.yml

@@ -20,9 +20,9 @@ jobs:
           fetch-depth: 0
 
       - name: Set up Node.js
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v4
         with:
-          node-version: '16'
+          node-version: '20'
 
       - name: Install Markdown Linter
         run: npm install -g markdownlint-cli