Update radios data-module to govuk-radios

This change is required due to new approach to namespacing[0] in V3.0 of
the GOV.UK Design System

[0] alphagov/govuk-frontend#1443

lib/govuk_design_system_formbuilder/containers/radios.rb

@@ -8,7 +8,7 @@ def initialize(builder, inline:, small:)
       end
 
       def html
-        @builder.content_tag('div', class: radios_classes, data: { module: 'radios' }) do
+        @builder.content_tag('div', class: radios_classes, data: { module: 'govuk-radios' }) do
           yield
         end
       end

spec/govuk_design_system_formbuilder/builder/radios_spec.rb

@@ -57,7 +57,7 @@
       end
 
       specify 'radio buttons should be surrounded by a radios module' do
-        expect(subject).to have_tag('div', with: { 'data-module' => 'radios' }) do |dm|
+        expect(subject).to have_tag('div', with: { 'data-module' => 'govuk-radios' }) do |dm|
           expect(dm).to have_tag('input', count: colours.size, with: { type: 'radio' })
         end
       end
@@ -193,7 +193,7 @@
       end
 
       specify 'output should contain radio buttons' do
-        expect(subject).to have_tag('div', with: { class: 'govuk-radios', 'data-module' => 'radios' }) do
+        expect(subject).to have_tag('div', with: { class: 'govuk-radios', 'data-module' => 'govuk-radios' }) do
           expect(subject).to have_tag('input', with: { type: 'radio' }, count: 2)
         end
       end