fix: update incorrect icons on gitlab duo page

Step 1: What is changing in this MR?

• referred from https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3631#include-any-graphic-or-design-assets to check the icons of the Git Suggestions and Code Suggestions cards

Production	Review app
https://about.gitlab.com/gitlab-duo/	https://3631-confidential-issue.about.gitlab-review.app/gitlab-duo/

Step 2: Ensure that your changes comply with the following, where applicable:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues.
• These changes work on both Safari, Chrome, and Firefox.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Build Variables:

• Use Contentful Preview API

Closes #3631