Install tumbler test in apertis-tests

This lets us run it from /usr/lib/apertis-tests/tumbler if desired.

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3488