[1.8.x] Refs #24652 -- Made sure template backend tests call their super setUpClass.

Backport of ead36e8a from master

tests/template_backends/test_dummy.py

@@ -18,6 +18,7 @@ class TemplateStringsTests(SimpleTestCase):
 
     @classmethod
     def setUpClass(cls):
+        super(TemplateStringsTests, cls).setUpClass()
         params = {
             'DIRS': [],
             'APP_DIRS': True,