chore(vue3): make test more focused and do not capture extra details

What does this MR do?

Vue3 and Vue2 render things a bit differently. Some attributes might be reordered, or some classes - nothing that changes actual HTML ordering, however makes snapshots and snapshot-like things fragile

This MR changes test to focus solely on thing-under-test (right what description states!) instead relying on entire component rendering output

This is forward-compatible change to support @vue/compat #1981 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • CustomersDot: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.