Remove specs violations from ProjectSelector

What does this MR do and why?

• Refactor with the goal to remove spec violations (Vue3 migration)
• Uses shallowMountExtended and getByTestid instead of querying js- classes

Screenshots or screen recordings

N/A

How to set up and validate locally

Run npm run jest -- -- spec/frontend/vue_shared/components/project_selector/project_list_item_spec.js

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 #391115 (closed)