Draft: CI: Add known-broken Fedora 43 configs

Fedora 43 was released two weeks ago on 2025-10-30. It brings with it GDK Pixbuf 2.44, which has a new Rust-based image loader named Glycin2 which is incompatible with the graphviz gdk plugin. (See issue #2732.) The plugin will silently produce empty files for any image exports attempted using it.

Since a test was added for this condition in !4555 (merged), it is expected that these Fedora 43 builds will fail until the gdk plugin is either fixed or disabled in Fedora 43 builds.

Marked as draft pending resolution of the above situation.

On the Fedora side, my PR to disable GDKPixbuf in graphviz builds on F43+ is still pending, but the maintainer has indicated intent to merge, so that will be the approach taken in the distro packages to address this (pending an upstream resolution here).