Adding the missing ` s right now.    Things that can be parsed as HTML are all over lua_api.txt, see e.g. [formspec docs](https://github.com/minetest/minetest/blob/454dbf83a9bf292910c1495a2aa49fd8b960c28f/doc/lua_api.txt#L438). I don't think me removing mine  individually would be of any value without a general 'no html syntax' rule for the docs.