Code highlighting is not always for the correct language

[jspenger]

The code highlighting seems to not always choose the correct language. See https://www.portals-project.org/vldb2023demo/shoppingcart. Ideally, this should be made more reliable. We also reuse this mechanism on the main portals website, so we should see to fix it as we start creating more content.

In short, the task is to make the automatic code highlighting (using hljs) reliably choose the language (most of the time we use Scala).