Don’t allow unstyled links

They should always be styled with the `govuk-link` class from GOV.UK
Frontend, or another custom class.

tests/app/main/views/test_accept_invite.py

@@ -453,7 +453,7 @@ def test_signed_in_existing_user_cannot_use_anothers_invite(
     assert page.h1.string.strip() == 'You’re not allowed to see this page'
     flash_banners = page.find_all('div', class_='banner-dangerous')
     assert len(flash_banners) == 1
-    banner_contents = flash_banners[0].text.strip()
+    banner_contents = normalize_spaces(flash_banners[0].text)
     assert "You’re signed in as test@user.gov.uk." in banner_contents
     assert "This invite is for another email address." in banner_contents
     assert "Sign out and click the link again to accept this invite." in banner_contents

tests/conftest.py

@@ -3030,6 +3030,7 @@ def client_request(
             if _test_for_elements_without_class and _expected_status not in (301, 302):
                 for tag, hint in (
                     ('p', 'govuk-body'),
+                    ('a', 'govuk-link govuk-link--no-visited-state'),
                 ):
                     element = page.select_one(f'{tag}:not([class])')
                     if (