Fix another CI_REGISTRY_IMAGE misname (used CI_REGISTRY by accident)

Author: lembergerth

.gitlab-ci.yml

@@ -116,7 +116,7 @@ unit-tests:llvm-3.9.1:
   stage: checks
   script: "ant $ANT_PROPS_CHECKS unit-tests-coverage"
   interruptible: true
-  image: "${CI_REGISTRY}/test:jdk-11"
+  image: "${CI_REGISTRY_IMAGE}/test:jdk-11"
   dependencies:
     - build-dependencies
     - build:llvm-3.9.1