Switch to PyQt6 by default about vimiv-qt

[jcjgraf]

Versions are just numbers, so in the end it does not really matter 🙃 However, I would strive for making that switch rather sooner than later, such that more people use Qt6 and potentially report related bugs.
The release of 1.0.0 will probably take some time as there are a few other things that should be finished up before, I guess?. So maybe it would make sense to make the switch in 0.10.0 and create that release rather soon (this week?) 🤔

[karlch]

Thanks for your thoughts! I agree with making the switch asap, and will prepare a PR tackling some of the remaining Qt6 issues opened over the past days including this then.

However, I am not sure it makes sense to rush the 0.10.0, yet. We should definitely not take as long as the last one, that was pretty horrid of a schedule 😆 but there is some more to do, and I would certainly like to run on Qt6 for a while before releasing with it.