Use confirm variant for 'New requirement' button

What does this MR do and why?

This MR uses the confirm variant for both New requirement buttons on the Requirements page because it's the correct action variant.

Screenshots or screen recordings

Before	After

How to set up and validate locally

(Make sure a GitLab Ultimate license is being used)

1. Go to a project
2. Go to Issues > Requirements
3. See the New requirement button in the confirm variant

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.