cpp: Reject signing expired keys
* lang/cpp/src/gpgsignkeyeditinteractor.cpp (enum SignKeyState): Add new state REJECT_SIGN_EXPIRED. (makeTable): Add entries for new state to transition map. (GpgSignKeyEditInteractor::action): Handle new state.
With this change the edit interactor aborts the key signing operation
with a "key expired" error instead of with a "general error".
- GnuPG-bug-id: T6155