The array-style does not pass GitHub Actions' linting. That form needs to be placed on a single line to have 0 lint warnings.

Also: add a name for the Job, which makes the output a little less cryptic.

* Fix scaffold controller generator with namespace

For example:

```
bundle exec rails g scaffold_controller Admin::Post title:string content:text --model-name=Post
```

It fixes the code generated by jbuilder, other changes are required on
railties gem.

* Specify main branch for rails-head

* Add test for controller scaffold with namespace

Only for Rails::VERSION::MAJOR >= 6 because the method `show_helper`
doesn't handle well the namespaces on previous versions.

Co-authored-by: David Heinemeier Hansson <[email protected]>