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.

web_src/css/base.css

@@ -1242,6 +1242,7 @@ overflow-menu .ui.label {
   white-space: pre-wrap;
   word-break: break-all;
   overflow-wrap: anywhere;
+  line-height: inherit; /* needed for inline code preview in markup */
 }
 
 .blame .code-inner {