They were already failing on master (with pango 1.47 and gjs 1.66):
(process:1186): Gjs-CRITICAL **: 12:36:09.500: JS ERROR: Error: Requiring Gtk, version 3.0: Typelib file for namespace 'HarfBuzz', version '0.0' not found
machine # @/nix/store/mca5jqi26f3h3s78p54bp59x4klyrch5-gjs-1.66.2-installedTests/libexec/installed-tests/gjs/js/testLegacyGObject.js:9:13
HarfBuzz is likely pulled in through Pango. Possibly introduced in https://github.com/NixOS/nixpkgs/pull/93799. But then why did not I notice that in GNOME 3.38 bump?
96fc9752af