dev-python/pygobject: fix missing test dep, die on test failures

dev-python/pygobject: fix missing test dep, die on test failures

The testing emake call had a missing "|| die", thus the test phase
only errored out if the last tested python version failed tests,
but not if earlier python version tests failed. This was observed
from pytest for python2.7 missing due to the missing dep and that
not being fatal.
Add the missing test dep.

Closes: https://bugs.gentoo.org/670184
Signed-off-by: Mart Raudsepp <leio@gentoo.org>
Package-Manager: Portage-2.3.52, Repoman-2.3.11