Fix reflow issue in vocabularies table

When increasing zoom to 400%, vocabularies table is impossible to get, since there's no scroll to get to it.

Steps to reproduce:
Set zoom to 400%
Login as an admin
Go to administration => vocabularies
Select a vocabulary

Expected:
I can access the vocabularies table with a 400% zoom.
See https://www.w3.org/TR/WCAG21/#reflow for context and how to meet the accessibility guidelines.