[BUGFIX] Convert fe_group in sys_collection to VARCHAR

The core methods dealing with frontend group restrictions expect this
field to be of a character based datatype. Comparing an integer based
field with string triggers query errors on PostgreSQL which
does not perform implict type conversions.

Resolves: #79447
Releases: master
Change-Id: Idc937e71d578e5f4a81595124c3aef53d32b2ed7
Reviewed-on: https://review.typo3.org/51392


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>