HorizontalTabsLabelsTest: Fix "createGroup" seemingly overriding previous created tabs.

Problem/Motivation

Currently, inside the "HorizontalTabsLabelsTest.php" "testHorizontalTabsLabelHtml" and "testHorizontalTabsLabelNoHtml" "createGroup()" seems to override the previous created tabs.

Steps to reproduce

Proposed resolution

Fix that.

Remaining tasks

User interface changes

API changes

Data model changes