Backport #23307 Close #23265, the code editor diff preview has been broken for long time. * Fix the regression for `data-line-num` * `.code-diff` is necessary to show the line number * Fix the regression for #12434 * The diff: [12434](https://github.com/go-gitea/gitea/pull/12434/files?diff=unified&w=1) * It hides the Type(4) (aka HunkHeader) for unexpected cases. Diff with ignoring whitespaces: https://github.com/go-gitea/gitea/pull/23307/files?diff=unified&w=1 Before: see the issue #23265 After:  Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
