Unfortunately the release of pygobject 2.28.4 was a bit premature, as it removed the workaround for the broken GLib.Variant.new_variant. This was only fixed in the yet unreleased g-i upstream git head, and not fixed at all in glib itself yet. Thus using the pygobject 2.28.4 release with the latest releases of glib and g-i is currently broken still.
Unfortunately the release of pygobject 2.28.4 was a bit premature, as it removed the workaround for the broken GLib.Variant. new_variant. This was only fixed in the yet unreleased g-i upstream git head, and not fixed at all in glib itself yet. Thus using the pygobject 2.28.4 release with the latest releases of glib and g-i is currently broken still.
I'll just cherrypick the patch for this then.