Qt6 on master

[Carl Schwan]

On Thursday, 14 September 2023 11:21:46 CEST you wrote:
> Hello,
> Yep we spoke with Volker this morning.
> We think to switch next week to qt6 in master => merging branch + adapt
> cmake I started to create script for it.
> We need to switch all in same time
> 
> If kleopatra needs qt5 you need to create it soon as we can't wait few
> months if we want to release pim-qt6 in start of next year as for other
> gear apps.

libkleo, kleopatra and mimetreeparser now have a kf5 branch. So we can safely 
move master to qt6 for these repos.

Cheers,
Carl