Pin markdown-link-check to v3.11.0 on GitHub Actions

Pin to v3.11.0 in GitHub Actions workflow to avoid false positive 404 
errors in CI.

Refs:
- tcort/markdown-link-check#250

.github/workflows/markdown-link-check.yml

@@ -18,6 +18,6 @@ jobs:
         with:
           node-version: 'lts/*'
       - name: Install markdown-link-check
-        run: npm i -g markdown-link-check
+        run: npm i -g markdown-link-check@3.11.0
       - name: Run markdown-link-check on MD files
         run: find . -name "*.md" | xargs -n 1 markdown-link-check -c markdown_link_check_config.json -q