Fix test_package_endpoint_throttling by clearing cache in setUp

The throttle cache was not being reset between test runs, causing
request counts from previous tests to spill over and trigger the
rate limit prematurely.

Fix by calling cache.clear() at the start of setUp().

Fixes #<replace-with-your-issue-number>

Author: clencyc

packagedb/tests/test_throttling.py

@@ -10,15 +10,17 @@
 from unittest.mock import patch
 
 from django.contrib.auth.models import User
-
+from django.core.cache import cache
 from rest_framework.test import APIClient
 from rest_framework.test import APITestCase
 
 
 @patch("rest_framework.throttling.UserRateThrottle.get_rate", lambda x: "20/day")
 @patch("rest_framework.throttling.AnonRateThrottle.get_rate", lambda x: "10/day")
 class ThrottleApiTests(APITestCase):
+
     def setUp(self):
+        cache.clear()
         # create a basic user
         self.user = User.objects.create_user(
             username="username",