cpp: Ensure that all transitions go from one state to a different state

* src/gpgsignkeyeditinteractor.cpp (makeTable): Replace transitions from
CONFIRM to CONFIRM with transitions from CONFIRM to CONFIRM2 and vice
versa. Add transitions from CONFIRM2 to some other state for all
transitions from CONFIRM to some other state.

The state machine gets stuck if a transition doesn't change the state
but an action is required. To avoid this situation the CONFIRM2 state
was introduced, but it was not used correctly.

Taken from gpgmepp commit aee2b30482406e677dbddf1a68b2a11a5dc70adf

• GnuPG-bug-id: T7600