Horizontal scrollbar is not shown when drag resizing columns

Steps to reproduce:

1. Enable Hierarchy V2 for the Scene Hierarchy
2. Resize any column large enough to make the horizontal bar visible

Actual results: 
The horizontal scrollbar is not shown

Expected results: 
The horizontal scrollbar is shown and update as the user drag-resize.

Reproducible with versions: 

6000.4, 6000.5

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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