According to https://git.gnome.org/browse/gtk+/log/?h=gtk-3-22 bugfix release 3.22.26 already available
Thank you for the bump request. You can help the maintainer with further information: Does a simple bump [1] work on your system? Chances are high, because a first look on the bump revealed only small changes. [1] https://wiki.gentoo.org/wiki/Custom_repository#Simple_version_bump_of_an_ebuild_in_the_local_overlay
It looks like that simple bump works.
Fixed in https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=a5dfb686bfacc26b3d446f9effcab54afa3aae8e