[BUGFIX] Add type definition for backend user section

Since columnsOverrides it is possible to overwrite TCA definitions
for specific columns and type combinations. However, as there is no
specific type definition for backend user sections, the default type
(and its overrides) were used. Backend user section was the only
undefined type. The type definition has now been added.

Resolves: #90577
Releases: master, 9.5
Change-Id: Ifded3bd9642afd7fffbb8918c9181ef1e3c7b6ea
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63482


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>