This is the base system for our CI, and the former mypaint-brushes
package got bumped to v2, which broke the build. Instead of rolling
back, they added a mypaint-brushes1 package. Let's rely on it instead of
installing it ourselves now.
If I get it correctly, archlinux bumped the mypaint-brushes package to
v2, which broke our CI. The v1 and v2 brushes are not the same, and they
are not even compatible (GIMP only supports v1 brushes so far). These
should be different packages, hence the incremented major versionning.
For the archlinux change, see also:
https://git.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/mypaint-brushes&id=dfd032b3aab40a46c751bd47713fb82bf11bd984
Let's just install the brushes ourselves from the correct branch.
With this kind of changes, as well as the weird patches they do when
they rename the pkg-config file of libmypaint, I think we should
consider not rely on this distribution for our CI.
We don't actually need any of the Python dependencies at runtime. We
only check for these to make packagers aware of the runtime need. Force
the build to go forward even with these deps.
Jehan