Make sure CI fails if any of the spec examples are tagged with :focus

rails_helper.rb

# spec/rails_helper.rb

RSpec.configure do |config|
  if ENV["CI"]
    config.before(:example, :focus) { raise "Should not commit focused specs" }
  else
    config.filter_run focus: true
    config.run_all_when_everything_filtered = true
  end
  
  # [...]
end