Vanilla flavor: Long lines overflowing in preformatted text (code blocks)

[sk22]

Steps to reproduce the problem

Post something like:

`​``
long line long line long line long line long line long line long line long line long line
`​``

(there's zero-width spaces so the code block on Github doesn't break)

Expected behaviour

The line should break, and not overflow

Actual behaviour

The line overflows when viewing using the vanilla flavor

Detailed description

Specifications

Catstodon v3.5.3+cat+1.1.1 Firefox 106.0.1 (Fedora 36)

[kescherCode]

Just tested to also occur in pure glitch-soc, so not caused by the Catstodon fork.