test(extras): Use cleanup handlers for config test teardown

Replace manual `clear_config()` and `cache.clear()` calls at test end
with `addCleanup()` registered in `setUp()`. Ensures cleanup runs even
if assertions fail mid-test, preventing Redis pollution across tests.

Fixes #22290

netbox/netbox/tests/test_config.py

@@ -10,22 +10,28 @@ CACHES = settings.CACHES
 CACHES['default'].update({'KEY_PREFIX': 'TEST-'})
 
 
+@override_settings(CACHES=CACHES)
 class ConfigTestCase(TestCase):
 
-    @override_settings(CACHES=CACHES)
-    def test_config_init_empty(self):
+    def setUp(self):
+        super().setUp()
+        # Register cleanup so it runs after each test, even on assertion failure.
+        # clear_config drops the thread-local Config; cache.clear wipes the Redis
+        # entries that configrevision.activate writes.
+        self.addCleanup(cache.clear)
+        self.addCleanup(clear_config)
+
+        # Defensive reset against pre-existing state from outside this class.
+        clear_config()
         cache.clear()
 
+    def test_config_init_empty(self):
         config = get_config()
         self.assertEqual(config.config, {})
         self.assertEqual(config.version, None)
 
-        clear_config()
-
-    @override_settings(CACHES=CACHES)
     def test_config_init_from_db(self):
         CONFIG_DATA = {'BANNER_TOP': 'A'}
-        cache.clear()
 
         # Create a config but don't load it into the cache
         configrevision = ConfigRevision.objects.create(data=CONFIG_DATA)
@@ -34,12 +40,8 @@ class ConfigTestCase(TestCase):
         self.assertEqual(config.config, CONFIG_DATA)
         self.assertEqual(config.version, configrevision.pk)
 
-        clear_config()
-
-    @override_settings(CACHES=CACHES)
     def test_config_init_from_cache(self):
         CONFIG_DATA = {'BANNER_TOP': 'B'}
-        cache.clear()
 
         # Create a config and load it into the cache
         configrevision = ConfigRevision.objects.create(data=CONFIG_DATA)
@@ -49,12 +51,9 @@ class ConfigTestCase(TestCase):
         self.assertEqual(config.config, CONFIG_DATA)
         self.assertEqual(config.version, configrevision.pk)
 
-        clear_config()
-
-    @override_settings(CACHES=CACHES, BANNER_TOP='Z')
+    @override_settings(BANNER_TOP='Z')
     def test_settings_override(self):
         CONFIG_DATA = {'BANNER_TOP': 'A'}
-        cache.clear()
 
         # Create a config and load it into the cache
         configrevision = ConfigRevision.objects.create(data=CONFIG_DATA)
@@ -63,5 +62,3 @@ class ConfigTestCase(TestCase):
         config = get_config()
         self.assertEqual(config.BANNER_TOP, 'Z')
         self.assertEqual(config.version, configrevision.pk)
-
-        clear_config()