Commit 18d3c529fa caused CI_HELPER to be
set to "''" (two single quotes), leading to an error when test.sh tries
to source $CI_HELPER.
CI_HELPER is not set anywhere else and not passed into the container
environment, so there is no need to test if it has a value.
This fixes the value of CI_HELPER.
Fixes: 18d3c529fa ("github-ci: error on any shell errors")
Signed-off-by: Jeffery To <jeffery.to@gmail.com>