[Flaky test] `RegistrationViewTestV2::test_rate_limiting_registration_view`

This test fails intermittently and will be deleted according to the Flaky Test Process in https://github.com/openedx/edx-platform/pull/36491

See docs on how to address flaky tests for why this should be fixed and how to go about it.

• Failing CI run, under openedx-2-with-lms(py=3.11,dj=pinned,mongo=7.0): https://github.com/openedx/edx-platform/actions/runs/14311302935/job/40106739835
• Subsequent Passing CI run: https://github.com/openedx/edx-platform/actions/runs/14311302935/job/40113340581

Failure output:

=================================== FAILURES ===================================
_________ RegistrationViewTestV2.test_rate_limiting_registration_view __________

self = <openedx.core.djangoapps.user_authn.views.tests.test_register.RegistrationViewTestV2 testMethod=test_rate_limiting_registration_view>

    @override_settings(
        CACHES={
            'default': {
                'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
                'LOCATION': 'registration_proxy',
            }
        }
    )
    def test_rate_limiting_registration_view(self):
        """
        Confirm rate limits work as expected for registration
        end point.
        Note that drf's rate limiting makes use of the default cache
        to enforce limits; that's why this test needs a "real"
        default cache (as opposed to the usual-for-tests DummyCache)
        """
        payload = {
            "email": 'email',
            "name": self.NAME,
            "username": self.USERNAME,
            "password": self.PASSWORD,
            "honor_code": "true",
        }
    
        for _ in range(int(settings.REGISTRATION_RATELIMIT.split('/')[0])):
            response = self.client.post(self.url, payload)
            assert response.status_code != 403
    
        response = self.client.post(self.url, payload)
>       assert response.status_code == 403
E       assert 400 == 403
E        +  where 400 = <JsonResponse status_code=400, "application/json">.status_code

openedx/core/djangoapps/user_authn/views/tests/test_register.py:1889: AssertionError
------------------------------ Captured log call -------------------------------
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
WARNING  django.request:log.py:241 Bad Request: /api/user/v2/account/registration/
=============================== warnings summary ===============================

Start with openedx/core/djangoapps/user_authn/views/tests/test_register.py at RegistrationViewTestV2::test_rate_limiting_registration_view, then run the targeted test and compare the provided failing and passing CI runs. Consult the linked Flaky Test Process and pull request 36491; done means the test is handled according to that process and no longer produces intermittent failures.