Don't run any stages without being triggered by tags.

.gitlab-ci.yml

@@ -1,14 +1,19 @@
 # This file is a template, and might need editing before it works on your project.
 # see https://docs.gitlab.com/ee/ci/yaml/README.html for all available options
 
-image: debian:stable
+variables:
+  DEFAULT_IMAGE: debian:stable
+
+default:
+  image: ${DEFAULT_IMAGE}
+  interruptible: true
+  only:
+    - tags
 
 before_script:
   - echo "Before script section"
   - echo "For example you might run an update here or install a build dependency"
   - echo "Or perhaps you might print out some debugging details"
-  - apt-get update
-  - apt-get -y install git dh-make build-essential autoconf autotools-dev
 
 after_script:
   - echo "After script section"
@@ -16,13 +21,13 @@ after_script:
 
 build1:
   stage: build
-  only:
-    - tags
   artifacts:
     paths:
       - build/*
   script:
     - echo "Do your build here"
+    - apt-get update
+    - apt-get -y install git dh-make build-essential autoconf autotools-dev
     - cp LICENSE debian/copyright
     - apt-get -y build-dep .
     - dpkg-buildpackage -uc -us