Update .gitlab/ci/build.gitlab-ci.yml, .gitlab/ci/deploy.gitlab-ci.yml, .gitlab/ci/test.gitlab-ci.yml files

.gitlab/ci/build.gitlab-ci.yml

@@ -7,3 +7,6 @@ build:
     name: multi_user
     paths: 
      - multi_user
+    only:
+     - master
+

.gitlab/ci/deploy.gitlab-ci.yml

@@ -17,3 +17,5 @@ deploy:
     - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
     - docker tag registry.gitlab.com/slumber/multi-user/multi-user-server:${VERSION} registry.gitlab.com/slumber/multi-user/multi-user-server:${CI_COMMIT_REF_NAME}
     - docker push registry.gitlab.com/slumber/multi-user/multi-user-server
+  only:
+    - master

.gitlab/ci/test.gitlab-ci.yml

@@ -3,3 +3,5 @@ test:
   image: slumber/blender-addon-testing:latest
   script:
     - python3 scripts/test_addon.py
+  only:
+    - master