Double dashes for command line flags turned into emdashes

[samdphillips]

Reported on Twitter
https://twitter.com/flyin1501/status/1531750602262204416

Specifically about this page https://blog.racket-lang.org/2022/04/racket-v8-5.html

[samth]

I think the problem there is that --enable-pb is not marked as code.