Add broken link checker on PR

.github/workflows/jekyll.yml

@@ -7,6 +7,7 @@
 name: Deploy Jekyll site to Pages
 
 on:
+  pull_request:
   # Runs on pushes targeting the default branch
   push:
     branches: ["master"]
@@ -47,6 +48,31 @@
         run: bundle exec jekyll build --baseurl "${{ steps.pages.outputs.base_path }}"
         env:
           JEKYLL_ENV: production
+
+      - name: Check for broken links
+        uses: athackst/htmlproofer-action@main
+        with:
+          directory: '_site'
+
+          check_images: false
+          check_scripts: false
+          check_opengraph: false
+
+          # External behavior
+          disable_external: false
+          enforce_https: false
+          ignore_status_codes: '403,429,500,502,503,504'
+
+          # Silence noise
+          check_internal_hash: false
+          check_external_hash: false
+          ignore_missing_alt: true
+          ignore_empty_alt: true
+          allow_missing_href: true
+
+          # Ignore HTTP + protocol-relative URLs
+          ignore_urls: '^http://,^//'
+
       - name: Upload artifact
         # Automatically uploads an artifact from the './_site' directory by default
         uses: actions/upload-pages-artifact@v3