ci: Enable FreeBSD CI
I worked around the RPATH bug of meson on the CI machine a few days ago, so I think we can safely enable FreeBSD CI now. I will put details of the current setup on Infrastructure/GitLab#286 (closed) for people who want to test or build the same environment themselves. Let's hope meson won't break seriously and lately again like what it happened in the 0.47.0 release.