Fix line height on inline code preview (#30372) (#30385)

Fix line height on inline code preview (#30372) (#30385)

Backport #30372 by @silverwind

Fixes https://github.com/go-gitea/gitea/issues/30353.

I don't know what causes `code-inner` to not inherit `line-height` from
its direct parent `.lines-code` but instead from grandparent `.markup`
even thought MDN tells me it's
[inherited](https://developer.mozilla.org/en-US/docs/Web/CSS/line-height#formal_definition).
This causes no negative impact on other code views, so I think it's the
best solution.

Co-authored-by: silverwind <me@silverwind.io>