specs: fix flaky "dossier brouillon" spec

When filling all the champs of a dossier, we skip the "Address"
champ (because it would attempt to request a blocked URL).

But that means the "Yes/No" radio buttons may be under the sticky
bottom bar, and thus not register the click – which makes the test fail.

Fix the issue by manually scrolling to the radio buttons.

spec/system/users/brouillon_spec.rb

@@ -23,6 +23,7 @@ describe 'The user' do
     choose('Madame')
     fill_in('email', with: 'loulou@yopmail.com')
     fill_in('phone', with: '0123456789')
+    scroll_to(find_field('Non'), align: :center)
     choose('Non')
     choose('val2')
     check('val1')