Item13242: UnifiedUserMapping: saner "temporary admin" logic

The previous logic, copied from ToppicUserMapping, set the user field in
the session to the super admin *group*. While, in principle, groups can
be treated as users, apparently, this is currently not accounted for in
UnifiedAuthContrib, so for now set the built-in admin account instead.

lib/Foswiki/Users/UnifiedUserMapping.pm

@@ -305,7 +305,7 @@ sub _getListOfGroups {
 
         # Temporarily set the user to admin, otherwise it cannot see groups
         # where %USERSWEB% is protected from view
-        local $this->{session}->{user} = $Foswiki::cfg{SuperAdminGroup};
+        local $this->{session}->{user} = 'BaseUserMapping_333';
 
         $this->{session}->search->searchWeb(
             _callback => \&_collateGroups,