Fix missing closing div tag around Related Posts in sidefoot

[Scotchester]

My bad: https://github.com/cfpb/cfgov-refresh/pull/4622/files#r416953702

Additions

• Re-adds accidentally removed closing </div> tag after including the Related Posts module in a sidefoot

Testing

1. Go to https://validator.w3.org/#validate_by_uri
2. Validate a page like https://www.consumerfinance.gov/about-us/blog/avoid-scams-find-help-during-quarantine/
3. Observe these errors toward the bottom of the list:
   
4. Pull branch
5. Load up http://localhost:8000/about-us/blog/avoid-scams-find-help-during-quarantine/
6. View source and copy it all
7. Go to https://validator.w3.org/#validate_by_input
8. Paste the source into the field and validate it
9. See that the aforementioned errors are not returned

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the CFPB development guidelines
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated
• Reviewers requested with the Reviewers tool ➡️