trigger only when tag

.gitlab-ci.yml

@@ -1,7 +1,6 @@
 variables:
   CI_PROJECT_DIR: "."
   CI_REGISTRY_IMAGE: hub.ducoterra.net/ducoterra/mysite
-  CI_COMMIT_TAG: 3.8.2_10
   DEPLOY: test
 
 stages:
@@ -10,6 +9,9 @@ stages:
   - deploy
 
 build:
+  only:
+    variables:
+    - $CI_COMMIT_TAG
   stage: build
   image:
     name: gcr.io/kaniko-project/executor:debug