Fix line height in lists (#1114)

An issue discovered by @fredrik-bakke — code blocks in lists inherit
bigger line spacing, making the ASCII diagrams more stretched.

Compare
![20240416 133603
screen](https://github.com/UniMath/agda-unimath/assets/15523887/20ff88b2-a26b-4153-9ffe-0a892fee5376)

theme/css/chrome.css

@@ -277,6 +277,7 @@ pre > .buttons button {
 }
 pre > code {
   padding: 1rem;
+  line-height: normal;
 }
 
 /* FIXME: ACE editors overlap their buttons because ACE does absolute