Math Markdown no longer working in in 10.5 RC3

As reported in https://gitlab.com/gitlab-org/gitlab-ce/issues/33573#note_58697008, try adding:

This math is inline a^2+b^2=c^2.

a^2+b^2=c^2

In the JavaScript console, I now see:

Request header field X-CSRF-Token is not allowed by Access-Control-Allow-Headers in preflight response.