app.ymlで、プラグインの stable ブランチをクローンしていますか?
はい、以下のように行います。
hooks:
after_code:
- exec:
cd: $home/plugins
cmd:
- git clone https://github.com/discourse/docker_manager.git
- git clone https://github.com/discourse/discourse-spoiler-alert.git
- git clone https://github.com/discourse/discourse-styleguide.git
- git clone --branch stable https://github.com/discourse/discourse-solved.git
- git clone https://github.com/discourse/discourse-user-notes.git
- git clone https://github.com/discourse/discourse-checklist.git
- git clone --branch stable https://github.com/discourse/discourse-assign.git