Bug#967719: fixed in qtractor 0.9.21-1

[Bastian Germann]

Okay, I see there is actually no gtk3 support.
I have added a commit that disables the GTKMM2 support, which can at least 
unblock #967497.
I do not think that gtkmm-2.4 will survive until trixie is released, so we 
should make the change as early as possible.
Please add a comment here if there is a really important reason to keep it.