Help windows in anaconda (Fedora installer) show no content with mutter 43.1

Fedora's openQA tests include one which runs the Fedora installer (anaconda) and tests opening the Help screen on every page. When you open a Help screen, anaconda runs a yelp process.

This test started failing on the "traditional" installer images in the Fedora-Rawhide-20221105.n.0 nightly compose. The test still passes on live images. The failure mode is that you see a "Help" window with a header bar but no actual content, just a grey blob:

On the "traditional" installer images, anaconda runs on gnome-kiosk, on X.org (not Wayland). So !2633 (merged) may well be involved here. In the 20221105.n.0 compose, anaconda did not change, and neither did yelp. webkitgtk did get updated, but we also pulled that update into the Fedora 37 RC-1.7 compose, and that compose does not have this bug, so that doesn't seem to be the culprit. mutter seems the likeliest culprit among things that changed on 20221105.n.0 and were not also pulled into the Fedora 37 RC-1.7 compose.