Fix line height on inline code preview (#30372)
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.
(cherry picked from commit 6cac11cb1bc4b42bc7851a59b1f3a94700c5eb84)
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