debian: run tests with VERBOSE=1

Make debbugging easier when tests are failing in the QA/CI system as we
can see what is actually failing.

Signed-off-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D4302