Instead of running the test directly in the build script, we can make a
separate step in the workflow so it looks a little prettier. For running
the actual tests, we skip mingw since they will never be run (cross
compiled). Additionally, improve the github workflow logic a bit so that
way logs on failure are only shown when that specific step fails. The
freebsd job still has to be less elegant since it's in a weird vm
thingy.
Not really related but the location of various build directories
(particularly waf) are corrected as well (might as well).
Since meson has its own unit testing system, let's rework mpv's tests so
they integrate nicely with this. To prepare for this, start off by
dropping the unittest option. Of course, this means that tests will no
longer be supported in the waf build at all but it will be dropped
anyway. Note that the tests option is preserved for the meson build. We
will still make use of this in the future commits.
