Don't add classes to the top level namespace

I've been writing too much Rust. My mind is still in the mode of things
being auto-namespaced based on the file...

activerecord/lib/active_record/connection_adapters/determine_if_preparable_visitor.rb

@@ -1,3 +1,5 @@
+module ActiveRecord
+  module ConnectionAdapters
     module DetermineIfPreparableVisitor
       attr_reader :preparable
 
@@ -16,3 +18,5 @@ def visit_Arel_Nodes_SqlLiteral(*)
         super
       end
     end
+  end
+end