refactor: migrate ENABLE_INSTRUCTOR_EMAIL and REQUIRE_COURSE_EMAIL_AUTH off FEATURES-as-dict

Three bulk_email test classes carried
`@patch.dict(settings.FEATURES, {'ENABLE_INSTRUCTOR_EMAIL': True,
'REQUIRE_COURSE_EMAIL_AUTH': False})`. Neither FEATURES key is read
anywhere in the platform or the installed packages anymore — bulk email
enablement is now governed by the BulkEmailFlag waffle flag and the
CourseAuthorization model — so these class-level overrides are vestigial
no-ops (and, being class-level `patch.dict`, only ever wrapped the
`test_*` methods, not setUp).

Both flags sit in a single decorator dict, so they migrate together:
convert to `@override_settings(ENABLE_INSTRUCTOR_EMAIL=True,
REQUIRE_COURSE_EMAIL_AUTH=False)`. Behavior is unchanged (still unread);
this just removes the FEATURES-dict usage. The classes subclass
SharedModuleStoreTestCase, so the class-level override_settings is valid.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: feanil

lms/djangoapps/bulk_email/tests/test_email.py

@@ -182,7 +182,7 @@ def mock_ugettext(text):
         return mail.outbox[0]
 
 
-@patch.dict(settings.FEATURES, {'ENABLE_INSTRUCTOR_EMAIL': True, 'REQUIRE_COURSE_EMAIL_AUTH': False})
+@override_settings(ENABLE_INSTRUCTOR_EMAIL=True, REQUIRE_COURSE_EMAIL_AUTH=False)
 @ddt.ddt
 class LocalizedFromAddressPlatformLangTestCase(SendEmailWithMockedUgettextMixin, EmailSendFromDashboardTestCase):
     """
@@ -210,7 +210,7 @@ def test_english_platform(self, language_code, enable_use_corse_id_in_from, ace_
             self.assertRegex(message.from_email, f'{language_code.upper()} .* Course Staff')  # noqa: PT009
 
 
-@patch.dict(settings.FEATURES, {'ENABLE_INSTRUCTOR_EMAIL': True, 'REQUIRE_COURSE_EMAIL_AUTH': False})
+@override_settings(ENABLE_INSTRUCTOR_EMAIL=True, REQUIRE_COURSE_EMAIL_AUTH=False)
 @ddt.ddt
 class AceEmailTestCase(SendEmailWithMockedUgettextMixin, EmailSendFromDashboardTestCase):
     """
@@ -268,7 +268,7 @@ def test_keyword_substitution_in_message_body(self):
         self.assertIn(f'Welcome to {self.course.display_name}', html_message_body)  # noqa: PT009
 
 
-@patch.dict(settings.FEATURES, {'ENABLE_INSTRUCTOR_EMAIL': True, 'REQUIRE_COURSE_EMAIL_AUTH': False})
+@override_settings(ENABLE_INSTRUCTOR_EMAIL=True, REQUIRE_COURSE_EMAIL_AUTH=False)
 @ddt.ddt
 class LocalizedFromAddressCourseLangTestCase(SendEmailWithMockedUgettextMixin, EmailSendFromDashboardTestCase):
     """