[gitlab-ci] only trigger readthedocs on branch/default

.gitlab-ci.yml

@@ -39,6 +39,9 @@ trigger-other-pipelines:
     - curl -X POST -F "variables[TRIGGERED_FROM_OTHER_PROJECT]=true" -F "token=$LOGILAB_DATABASE_PIPELINE_TRIGGER_TOKEN" -F ref=branch/default https://forge.extranet.logilab.fr/api/v4/projects/248/trigger/pipeline -w "\nhttp code:"\ "%{http_code}\n" -f
 
 trigger-readthedocs:
+  only:
+    refs:
+      - branch/default
   stage: after-tests
   script:
   # regarding the " everywhere when there is a '%': yaml is extremly weird when % are involved