there aren't any instance method defined in this class

* Run actionpack and actioncable tests together
* Demote ac:integration to allow_failures -- it works most of the time,
  but still fails too frequently to rely upon

[ci skip]

Fix duplicable? for Complex and Rational

quiet generators log in test

Remove warning in ActiveJob

This quiet the following log.

```
   create  app/mailers/notifier_mailer.rb
   invoke  erb
   create    app/views/notifier_mailer
identical    app/views/layouts/mailer.text.erb
identical    app/views/layouts/mailer.html.erb
   create    app/views/notifier_mailer/foo.text.erb
   create    app/views/notifier_mailer/foo.html.erb
   invoke  test_unit
   create    test/mailers/notifier_mailer_test.rb
   create    test/mailers/previews/notifier_mailer_preview.rb
```

Currently it causes:

```
activejob/Rakefile:5: warning: already initialized constant ACTIVEJOB_ADAPTERS
```

Document and update API for `skip_parameter_encoding`