Replace divs with sections

What does this MR do and why?

For the use case in hand, semantically it's more correct to use section instead of div. This MR replaces these divs with sections.

Screenshots or screen recordings

Nothing changes visually but here's a screenshot that it works properly:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Navigate to /-/security/vulnerabilities/new through the URL (should be a project scope)
2. Check whether the page renders properly or not.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #349864 (closed)