[CI] #97: Trigger PyPi release job only on tag

- Prevents the creation of two jobs: one from the tag and the other from the commit
- Might fix non-working PyPi releases not made from the job with the tag

.gitlab-ci.yml

@@ -96,6 +96,8 @@ release:
     - pip install -r requirements_deploy.txt
     - make build
     - make deploy PYPI_LOGIN=${PYPI_LOGIN} PYPI_PASSWORD=${PYPI_PASSWORD}
+  only:
+    - tags
 
 release_test:
   <<: *pyenv