Fix association scope constraining
Fix association scope constraining

Before this, a call to `pen.product.specific` would call
ActsAs::QueryMethods#where with `opts = { “pens” => { “id” => “1” } }`
to establish an association scope constrained to the specific pen, but
our implementation of `where` would then mutate opts into `opts = {
“products” => { “pens” => { “id” => “1” } } }` (invalid), since
`attribute_method?(“pens”) == false`

NuffieProductions/active_record-acts_as,krautcomputing/active_record-acts_as,hzamani/active_record-acts_as