[Flaky test] `openedx/core/djangoapps/user_authn/views/tests/test_login.py::LoginTest::test_login_ratelimited`

This test fails intermittently and has been deleted according to the Flaky Test Process in https://github.com/openedx/edx-platform/pull/25096

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

• It failed and passed on the same commit on this PR: https://github.com/edx/edx-platform/pull/25082
• Failed build in Jenkins: https://build.testeng.edx.org/job/edx-platform-python-pipeline-pr/21935/

Failure output:

self = <openedx.core.djangoapps.user_authn.views.tests.test_login.LoginTest testMethod=test_login_ratelimited>

    def test_login_ratelimited(self):
        """
        Test that login endpoint is IP ratelimited and only allow 5 requests
        per 5 minutes per IP.
        """
        for i in range(5):
            password = u'test_password{0}'.format(i)
            response, _audit_log = self._login_response(self.user_email, password)
            self._assert_response(response, success=False)
    
        response, _audit_log = self._login_response(self.user_email, self.password)
>       self.assertEqual(response.status_code, 403)
E       AssertionError: 200 != 403

openedx/core/djangoapps/user_authn/views/tests/test_login.py:396: AssertionError

Migrate from private ticket https://2u-internal.atlassian.net/issues/CR-2761

Start with openedx/core/djangoapps/user_authn/views/tests/test_login.py and the deleted LoginTest::test_login_ratelimited test. Review the linked flaky-test process and the failure from PR 25082, then trace the rate-limit setup used by the test. Done means the login rate-limit behavior is covered reliably and the test no longer intermittently returns 200 instead of 403.