build(deps): bump actions/checkout from 4 to 5 in the gh-actions group

Bumps the gh-actions group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 4 to 5
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: gh-actions
...

Signed-off-by: dependabot[bot] <support@github.com>

_includes/sidebar.html

@@ -52,13 +52,21 @@
     {% endunless %}
 
     {% for entry in site.data.contact %}
+      {%- assign url = null -%}
+
       {% case entry.type %}
         {% when 'github', 'twitter' %}
+          {%- unless site[entry.type].username -%}
+            {%- continue -%}
+          {%- endunless -%}
           {%- capture url -%}
             https://{{ entry.type }}.com/{{ site[entry.type].username }}
           {%- endcapture -%}
         {% when 'email' %}
-          {% assign email = site.social.email | split: '@' %}
+          {%- unless site.social.email -%}
+            {%- continue -%}
+          {%- endunless -%}
+          {%- assign email = site.social.email | split: '@' -%}
           {%- capture url -%}
             javascript:location.href = 'mailto:' + ['{{ email[0] }}','{{ email[1] }}'].join('@')
           {%- endcapture -%}