gtk3 update, to fix opengl problems with software rendering

[Rene Hopf]

Hi,

there was a problem with gtkglarea when using software rendering: 
https://gitlab.gnome.org/GNOME/gtk/-/issues/64

I submitted a patch to gtk, which has been merged into the gtk-3-24 branch.

https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/1868

It would be great if all gtk3 packages for Debian could be updated to 
include this fix.

Rene