[BUGFIX] Missing icons for some core db tables

The records of EXT:extensionmanager are also set to adminOnly=TRUE

Resolves: #56808
Releases: 6.2
Change-Id: I79f7dae056c8ede8e041f71200dc1f88b7a5551c
Reviewed-on: https://review.typo3.org/28290
Reviewed-by: Wouter Wolters
Reviewed-by: Markus Klein
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring