Fixes https://github.com/thoughtbot/administrate/issues/1978 https://github.com/thoughtbot/administrate/issues/2209
At lib/administrate/field/associative.rb, we are currently using the wrong incantation to figure out the name of the associated class. What we have works most of the time, but will drop the namespace if there's one.
For example: if Blog::Post.has_many :tags of type Blog::Tags, it will incorrectly guess that the class name of :tags is "Tag" instead of "Blog::Tag".
This breaks the Blog::PostDashboard, which thinks it has to link to TagDashboard instead of Blog::TagDashboard.
The fix is just the one liner in that file. The rest is putting together an instance of this in the example app, and a spec to test it.