Add specs for hidden groups item component

What does this MR do?

Add some more specs for hidden_groups_item.vue:

• Make sure the correct text gets displayed
• Check the icons (folder and help) are there
• Test that the tooltip is wired up correctly

See gitlab-com/www-gitlab-com#5754 (comment 482376754) for more context.

Screenshots (strongly suggested)

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