Rendered item processor stores roles as associative array in config

A (small) error we already fixed in a lot of places seems to have still slipped through in the Rendered Item processor: the roles configuration key there is an associative array instead of a plain (numerically indexed) list.

For some reason, we explicitly have orderby: key in our schema definition for that config key, but I’m pretty sure it’s still a mistake. (Also, no discussion of that key in #2860167: Add "orderby" to our config schema definitions, where the schema line was added.) Just switching this to orderby: value should already do the trick.