CI: put docs from both 1.0 and master on pages

Done by building from two branches in same job.

Looks like this:

• https://pvir.pages.freedesktop.org/pipewire/
• https://pvir.pages.freedesktop.org/pipewire/devel/
• https://gitlab.freedesktop.org/pvir/pipewire/-/pipelines/1141843
• https://gitlab.freedesktop.org/pvir/pipewire/-/pipelines/1141851

This would also need to go to the 1.0 branch.