Fixes https://github.com/go-gitea/gitea/issues/24253
When a tasklist checkbox is clicked, the tasklist code [updates
`.raw-content` with latest server
data](7a8fe9eb37/web_src/js/markup/tasklist.ts (L73))
in the DOM after POSTing.
Then when "Edit" is clicked the ComboMarkdownEditor is shown with a
stale value from the previous edit session.
The fix makes it always read from `.raw-content`, no server
syncronization necessary because the value in `.raw-content` is the
latest from the server.
---------
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
2896dac536