[ci] test release branches

.gitlab-ci.yml

@@ -13,7 +13,7 @@ workflow:
     - if: $CI_PIPELINE_SOURCE == "schedule"
     - if: $CI_PIPELINE_SOURCE == "pipeline"
     - if: $CI_PIPELINE_SOURCE == "merge_request_event"
-    - if: $CI_COMMIT_BRANCH == "master"
+    - if: '$CI_COMMIT_BRANCH =~ /^(master|releases\/)/'
 
 # for commits happening on master, we check if there was a successful
 # pipeline on a related merge request already. If yes, we simply return
@@ -26,7 +26,7 @@ check-pipeline-status:
       when: never
     - if: $CI_PIPELINE_SOURCE == "pipeline"
       when: never
-    - if: $CI_COMMIT_BRANCH == "master"
+    - if: '$CI_COMMIT_BRANCH =~ /^(master|releases\/)/'
       when: always
   script:
     - |