it is probably that pygobject 2.90.4 is actually pygobject-3.0 also 2.90.4 is a beta version
most of the gnome projects obey some versioning rules, a few notes from my experince with gnome:
any major version ending with odd numbers are development branch and even numbers are stable for example pygobject 2.27 is dev branch but 2.26 is stable
when 2.27 is going to be released as 2.28 they start numbering it like 2.27.90.x which they call beta releases and anything like 2.27.97, 2.27.98 or even 2.27.999 is called release candidate
so you must stick with 2.28 stable branch till tc moves to gtk3