Improve codebase quality (#19999)

Small PR that improves the overall quality of the codebase. It's a bit
of everything:

1. Using correct variants for the variants we are testing
2. Use `@reference` instead of `@import` in a test, testing the
`@reference` according to the test name
3. Use `using` for Vitest related mocks. They have a `Symbol.dispose`
implemented, so we can don't have to restore mocks ourselves (right now,
some of them are not cleaned up at all).
4. Updated deprecated `.toThrowError` with `.toThrow` APIs

## Test plan

Everything still passes.

[ci-all]