Replace isEmpty() check with other expectations

What does this MR do?

As simple as it is. @vue/test-utils 1.x deprecate .isEmpty().

This MR replaces all expect(something.isEmpty()).toBe(false) with meaningful assertions or drop them if they make no sense in the context of the test

See !40213 (merged) for false counterpart of this MR :)

No other changes :)

See &3856 (closed) for details

Screenshots

N/A

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done