Update .gitlab-ci.yml file, use sha to pin version

.gitlab-ci.yml

@@ -20,4 +20,4 @@ container:
       /kaniko/executor
       --context "${CI_PROJECT_DIR}"
       --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
-      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG}"
+      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_SHORT_SHA}"