Runtime Update

[Justinzobel]

Please consider upgrading to a Qt6 runtime if your application supports Qt6, or 5.15-2308 otherwise.

[Green-Sky]

To add more to what I did:
I finally added the EOL notice, I updated to the qt5 lts and repointed toktok repo (since the offical repo is read-only now and I needed patches for the qt5 lts move).

Since then there has emerged an experimental qt6 port there aswell TokTok/qTox#49 , but that is not in the flatpak (yet?).

[Green-Sky]

FYI, I am going to remove the EOL notice soon again, after development picked up again at TokTok.