String freeze exception for kmail account wizard

[Carl Schwan]

Hi,

During the Qt5 to Qt6, the KMail account wizard had to be almost rewritten, 
unfortunately there are many major regression that made it to the RC.

I'm been spending the last few days fixing these and also clean it up a bit 
here: https://invent.kde.org/pim/kmail-account-wizard/-/merge_requests/19

This ads to a few more strings particularly around error handling, I hope this 
is fine.

Cheers,
Carl