The more files we use from the $srcdir, the more likely it is that
test fixes can be deployed to LAVA without waiting for a package
rebuild.

Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3634