Update validate_markdown.yml

.github/workflows/validate_markdown.yml

@@ -12,6 +12,10 @@ jobs:
     - name: Check out code
       uses: actions/checkout@v4.1.0
 
+    # https://github.com/actionshub/markdownlint
+    - name: Markdown Lint
+      uses: actionshub/markdownlint@main
+
     # https://github.com/marketplace/actions/markdownlint-cli2-action
     - name: Identify changed files
       uses: tj-actions/changed-files@v41