Assume less in the on_unload callback for AR scopes

Please check the comment in the patch for details.

Thanks to @casperisfine for suggesting this refactor.

activerecord/lib/active_record/railtie.rb

@@ -394,7 +394,11 @@ To keep using the current cache store, you can turn off cache versioning entirel
       config.after_initialize do
         unless app.config.cache_classes
           Rails.autoloaders.main.on_unload do |_cpath, value, _abspath|
-            value.current_scope = nil if value.is_a?(Class) && value < ActiveRecord::Base
+            # Conditions are written this way to be robust against custom
+            # implementations of value#is_a? or value#<.
+            if Class === value && ActiveRecord::Base > value
+              value.current_scope = nil
+            end
           end
         end
       end

railties/test/application/initializers/frameworks_test.rb

@@ -342,8 +342,25 @@ module ApplicationTests
     test "Current scopes in AR models are reset on reloading" do
       rails %w(generate model post)
       rails %w(db:migrate)
+
+      app_file "app/models/a.rb", "A = 1"
+      app_file "app/models/m.rb", "module M; end"
+      app_file "app/models/post.rb", <<~RUBY
+        class Post < ActiveRecord::Base
+          def self.is_a?(_)
+            false
+          end
+
+          def self.<(_)
+            false
+          end
+        end
+      RUBY
+
       require "#{app_path}/config/environment"
 
+      A
+      M
       Post.current_scope = Post
       assert_not_nil ActiveRecord::Scoping::ScopeRegistry.current_scope(Post) # precondition