Syntax highlight fails with `%r/` Ruby expression
### Summary Ruby syntax highlight fails with `%r` Ruby expression. See screenshot of https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/models/project.rb ### Screenshot ![image](https://gitlab.com/-/project/278964/uploads/3b65e2ff22590fd818ba6fa82c8ce813/image.png){width=825 height=494}
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