UI: Force Wayland usage under Wayland session

Qt doesn't use the Wayland platform on GNOME, so we have to
force it using the QT_QPA_PLATFORM env var. It's still possible to
use other QPA platforms using this env var, or the -platform command
line option.

qt5-wayland is now a required dependency for OBS on Linux (or FreeBSD).

Co-authored-by: Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f