fixed email address for missed certification section

Misused term (or terms)

• learning@

Alternatives

• learning@gitlab.com

Reason why

In the Missed certification section, the email address is not completed, so that user might not know what email address domain they should send to.

Author checklist

• Named the MR appropriately
• Reviewed how it renders on the Top Misused Terms page
• Submit for review

Review process

• Assign to any GitLab team member for initial review and approval.