Prevent importing from @gitlab/ui/dist in test files

What does this MR do and why?

Prevent importing from @gitlab/ui/dist in test files

Depends on !201730 (merged).

As gitlab builds gitlab-ui from source, this change prevents our test files from containing references to @gitlab/ui/dist that should not be part of our build.

References

• Related issue: #554202 (closed)

Screenshots or screen recordings

NA

How to set up and validate locally

A green pipeline and (no changes to app/assets/builds/tailwind.css) should be enough.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #554202 (closed)