Only do anything CI/CD with docker on the master branch

.gitlab-ci.yml

@@ -7,6 +7,9 @@ stages:
 auth-job:
   stage: auth
   image: docker:stable
+  only:
+    refs:
+      - master
   script:
     - docker login --username "$REGISTRY_USER" --password "$REGISTRY_PASSWORD" "$REGISTRY_BASE_URL"
     - cp "/root/.docker/config.json" "./build/.dockerconfigjson"
@@ -17,6 +20,9 @@ auth-job:
 build-job:
   stage: build
   image: docker:stable
+  only:
+    refs:
+      - master
   tags:
     - docker
   script:
@@ -25,6 +31,9 @@ build-job:
 publish-job:
   stage: publish
   image: docker:stable
+  only:
+    refs:
+      - master
   needs:
     - auth-job
     - build-job