The same behavior can be examined with the Infobox on https://en.wikipedia.org/wiki/Vala_(programming_language) with a viewport wide enough to bring a code block high enough on the screen.

OS: Windows 10 Version 20H2
Browser: Microsoft Edge (Chromium-based) Version 88.0.705.56 (Official build) (64-bit)

Removing the code block's parent <div> and adding its attributes to the child <pre> tag seems to resolve the issue, but being generally unfamiliar with MediaWiki I am not sure how feasible this is.

If the parent <div> is necessary, it also seems that setting the display: contents; property also achieves the same thing as by design this treats the <div> element as if it doesn't exist visually while allowing its children to inherit its properties. This seems to be the desired option in this scenario if removing the <div> isn't feasible.