schema: fix incorrectly nested prop in settings

Created by: LawnGnome

This was introduced in #8059, but appears to have been placed in the wrong part of the schema document. Since this setting is only used by the web frontend, and it's accessed from a object by its string key, there should be no functional change, besides the slim chance that a user has a non-boolean value at present, and the user settings textarea now autocompleting for search.hideSuggestions.