Upgrade sensiolabs/security-checker from 5 to 6
Upgrade sensiolabs/security-checker from 5 to 6

The conflict issue occurred during the installation of one of the SilverStripe modules
where one of its dependencies requires symfony/event-dispatcher v5 which conflicts with
symfony/console[v4.4.7]. For reference, sensiolabs/security-checker v5.0.3 requires
symfony/console (~2.7|~3.0|~4.0).

spekulatius/silverstripe-composer-security-checker