`test_login_workflow_with_mfa_enabled` is flaky

Example failure log:

```
=================================== FAILURES ===================================
_____________________ test_login_workflow_with_mfa_enabled _____________________
[gw0] linux -- Python 3.12.12 /home/runner/.cache/pypoetry/virtualenvs/flagsmith-api-h9Rv37Cj-py3.12/bin/python

db = None, api_client =

def test_login_workflow_with_mfa_enabled(
db: None,
api_client: APIClient,
) -> None:
email = "test@example.com"
password = FFAdminUser.objects.make_random_password()
register_data = {
"email": email,
"password": password,
"re_password": password,
"first_name": "test",
"last_name": "user",
}
register_url = reverse("api-v1:custom_auth:ffadminuser-list")
register_response = api_client.post(register_url, data=register_data)
> assert register_response.status_code == status.HTTP_201_CREATED
E assert 400 == 201
E + where 400 = .status_code
E + and 201 = status.HTTP_201_CREATED

tests/integration/custom_auth/end_to_end/test_custom_auth_integration.py:233: AssertionError
----------------------------- Captured stderr call -----------------------------
django.request WARNING Bad Request: /api/v1/auth/users/
------------------------------ Captured log call -------------------------------
WARNING django.request:log.py:253 Bad Request: /api/v1/auth/users/
```