Update docs targeting 12.3

doc/api/labels.md

@@ -188,7 +188,7 @@ Example response:
 
 ## Promote a project label to a group label
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25218) in GitLab 11.9.
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25218) in GitLab 12.3.
 
 Promotes a project label to a group label.
 

lib/api/labels.rb

@@ -64,7 +64,7 @@ module API
       end
 
       desc 'Promote a label to a group label' do
-        detail 'This feature was added in GitLab 11.9'
+        detail 'This feature was added in GitLab 12.3'
         success Entities::GroupLabel
       end
       params do