Emphasize lines are duplicated in formatted files

[cbullinger]

Emphasize lines are sometimes duplicated in formatted .rst and .md files. The outputted file displays correctly so this is low priority, but it would be nice to figure out why it's occurring. I don't see an obvious pattern as to which line #s are duplicated.

See https://github.com/mongodb/docs-realm/pull/3068#discussion_r1383613756 for example