Qt 6.9 Beta CI added to KDE Frameworks

[Albert Astals Cid]

Today we have added a Linux Qt 6.9 Beta CI build to KDE Frameworks in the 
shape of the linux-qt6-next.yml template

It compiles with Qt 6.9 Beta 1 packages (krop is working in updating them to a 
newer snapshot of the 6.9 branch).

We have done this to try to catch potential Qt regressions by using our tests 
(we have found none so far, so "yay?" I guess :D)

The new builds have the "platform flavour" of Linux/Qt6Next so if we find 
ourselves that some tests are failing and we think it's a regression we can 
disable the MRs failing by switching

  require-passing-tests-on: [ 'Linux' ]

to

  require-passing-tests-on: [ 'Linux/Qt6' ]

and that will exclude Linux/Qt6Next from marking builds as failed if tests 
fail, but before doing that, please contact me so we can try to figure out 
what's going on.

Please wait before adding this template to other projects outside of KDE 
Frameworks, e.g. we want to add this to KDE Gear, but there's lots of KDE Gear 
and we don't want to overload the servers.

We are going to get a new builder hardware (sponsored by The Qt Company) in 
less than a month, once that happens we can add the template to all the 
repositories that we want.

Cheers,
  Albert