Callouts are copy/pastable again

[dmlloyd]

Something changed with the syntax highlighter, and now callouts are selectable again.

Commit 9748156 attempted to fix this by making b tags of class conum non-selectable. However, the b tag enclosing the callout no longer carries this class. This might be a highlightjs bug or an asciidoctor bug.

It's possible that 933173b introduced this bug (/cc @antoinesd).

See also quarkusio/quarkus#1653

[dmlloyd]

Fixed via #147.