Use images from Docker Hub is very slow

It seems it is becoming worse.

I did some tests:

• it seems that using registry.gitlab.gnome.org/claudioandre/gjs:image can make CI run much faster.
• unfortunately, I was banish from gitlab.gnome.org for a few hours after pushing one image.

Not sure if a maintenance happened and the events are not connected. Anyway, I'll create a MR and try to push images again to see if I will be banned again.