Update .gitlab-ci.yml: set DETECTOR_CONFIG to DETECTOR if unset

If DETECTOR is set but DETECTOR_CONFIG is not, then we cannot set DETECTOR_CONFIG reliably.

.gitlab-ci.yml

@@ -62,7 +62,7 @@ common:setup:
           export JUGGLER_DETECTOR="ecce" 
         fi
         if [[ "${JUGGLER_DETECTOR_CONFIG}" == "" ]] ; then
-          export JUGGLER_DETECTOR_CONFIG="${JUGGLER_DETECTOR_CONFIG}"
+          export JUGGLER_DETECTOR_CONFIG="${JUGGLER_DETECTOR}"
         fi
         if [[ "${JUGGLER_DETECTOR_VERSION}" == "" ]] ; then
           export JUGGLER_DETECTOR_VERSION="main"