Fix markdown linting to use Rakefile task instead of hardcoded command

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: GarthDB

.github/workflows/jekyll.yml

@@ -48,7 +48,7 @@ jobs:
         run: npm ci
 
       - name: Lint Markdown
-        run: bundle exec mdl ./ -r ~MD002,~MD013,~MD026,~MD028,~MD029,~MD032,~MD033,~MD034
+        run: bundle exec rake markdown_lint
 
       - name: Lint SCSS
         run: npm run stylelint