Backport https://github.com/go-gitea/gitea/pull/25184 by @jtran
Closes#25225.
Fixes https://github.com/go-gitea/gitea/issues/25160.
`data-source-position` of checkboxes in a task list was incorrect
whenever there was YAML front matter. This would result in issue content
or PR descriptions getting corrupted with random `x` or space characters
when a user checked or unchecked a task.