nixos/tests/quake3: Fix eval due to unfree license

Regression introduced by 6b447a3c.

In this commit the Quake 3 demo data now have a meta attribute which
specifies the license as unfreeRedistributable.

While I haven't found anything official about that on the web, let's
just allow it to be used in the test because first of all, we have been
using it for a long time (since 2009, introduced in 497760b4

) and second,
because it will be quite some effort to rewrite the test with something
like OpenArena (particularily because we need coverage data and need to
use the ioquake3 version plus OpenArena-specific patches).

Tested evaluation on my local system, but the VM test still fails.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>