temp/gtk4.0: upgrade to 4.13.6

@Newbyte @tpikonen

I think this might be worth testing ahead? Providing them with early feedback might make our life much easier in the long-run, that if we only catch regressions after the stable release. But will certainly break something or need adjustments for some devices. What do you think?

Overview of Changes in 4.13.6, 25-01-2024
=========================================

This release changes the ngl renderer to be the default renderer.

The intent of this change is to get wider testing and verify that
the new renderers are production-ready. If significant problems
show up, we will revert this change for 4.14.

You can still override the renderer choice using the GSK_RENDERER
environment variable.

Since ngl can handle fractional scaling much better than the old gl
renderer, we allow fractional scaling by default with gl now. If you
are using the old gl renderer (e.g. because your system is limited to
GLES2), you can disable fractional scaling by setting the GDK_DEBUG
environment variable to include the gl-no-fractional key.