Fix `ActiveRecord::RecordNotFound` error message with custom primary key


```ruby
class User < AR::Base
   self.primary_key = :name
end

# Before:
User.find 'Hello World!'
# => ActiveRecord::RecordNotFound: Couldn't find Toy with name=Hello World!
User.find 'Hello', 'World!'
# => ActiveRecord::RecordNotFound: Couldn't find all Toys with IDs (Hello, World!) (found 0 results, but was looking for 2)


# After:
User.find 'Hello World!'
# => ActiveRecord::RecordNotFound: Couldn't find Toy with name=Hello World!
User.find 'Hello', 'World!'
# => ActiveRecord::RecordNotFound: Couldn't find all Toys with NAMEs (Hello, World!) (found 0 results, but was looking for 2)

```