Kamoso + Qt6

[Aleix Pol]

Hi releasers,
Today after much work I merged the Qt 6 MR in Kamoso

This included work upstream in GStreamer [1]. This work got merged but
it hasn't been released yet (and it won't be for almost a year as it's
in 1.27.1 and the public one will be 1.28.0).

Since we need this on Kamoso's release, there's some options:
- I requested (without much hope) to have it backported to 1.26.
- we ask distros to backport the patch (? much like it's doing in the
.flatpak-manifest.json)
- we release from the Qt5 branch until GStreamer releases
- we try to workaround in a different way that I don't know about.

Aleix

[1] https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9085#note_2959144