Properties Editor is a bit more picky (compared to the Outliner for example) when it comes to listening to grease pencil notifiers -- it requires the action to be set. So when adding the notifier in the dopesheet from the channels (done in `achannel_setting_flush_widget_cb`), now add the `NA_EDITED` action. Maniphest Tasks: T87640 Differential Revision: https://developer.blender.org/D11025