When the Key Type is not forced we correctly update key usage depending on the subkey selection.

But in case we have

[CertificateCreationWizard][$i]
PGPKeyType=

In the config the usage is not correctly forced. This leads to the situation where the user can uncheck all usage checkboxes for the certficiate except certify, which then results in a general error because the subkey is forced.

I would just also make the usage checkboxes read only when PGPKeyType is forced. For now we don't have a usecase for forced usage differences.