build docs on master as well

.gitlab-ci.yml

@@ -27,6 +27,7 @@ variables:
     - if: $CI_PIPELINE_SOURCE == "external_pull_request_event"
       when: never
     - if: $CI_COMMIT_BRANCH == "develop"
+    - if: $CI_COMMIT_BRANCH == "master"
     - if: $CI_COMMIT_TAG =~ /^v/
 
 .global_trigger_full_tests: &global_trigger_full_tests