Don’t spellcheck email addresses

The GOV.UK Design System recommends:
> setting the spellcheck attribute to false so that browsers do not
> spellcheck the email address

tests/app/main/views/test_register.py

@@ -15,6 +15,7 @@ def test_render_register_returns_template_with_form(client):
     assert response.status_code == 200
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
     assert page.find('input', attrs={'name': 'auth_type'}).attrs['value'] == 'sms_auth'
+    assert page.select_one('#email_address')['spellcheck'] == 'false'
     assert 'Create an account' in response.get_data(as_text=True)