Update scoped labels end-to-end test to cover another scenario

What does this MR do?

The idea is to increase the test coverage of enterprise features.

For reference, this is the feature being covered with the updated test: https://docs.gitlab.com/ee/user/project/labels.html#labels-with-multiple-colon-pairs

This MR is related to &1669.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content