build: Replace missing crates.io dependency with Purism-hosted one

This half-fixes the build (debian future is still broken).

A dependency of gio was pulled, meaning that vanilla non-Debian builds stopped working.

I pulled the offending package into my user's namespace at Purism, and that's probably not the right place in the long term. @guidog what do you think? Should "fragile" repo live at gitlab.gnome.org?