[ci] only execute check-no-changes-in-data in MR targetting master

.gitlab-ci.yml

@@ -68,6 +68,8 @@ check-no-changes-in-data:
     - echo "Checking that git status output is empty..."
     - sh -c '[ "`git status -s`" = "" ]'
     - git diff --exit-code
+  only:
+    - merge_requests
 
 generate-access-history:
   extends: .template-refrepo