Make cards in app/views/projects/imports/new.html.haml Pajamas-compliant

What does this MR do and why?

This MR updates a custom card component to Pajamas::AlertComponent for displaying the project.import_failed error.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Visit Menu -> Projects -> Create new project -> Import project.
2. Select GitLab export.
3. Fill in the form and upload an empty .gz file to the GitLab project export field.
4. The error message will appear at the top.

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.

Review progress:

• UX review
• frontend developer review
• frontend maintainer review

Related to #367126 (closed)