Added multi_db=True to test cases that access the 'other' db connection.

Fixed a failure in the context processors tests when running in
reverse on MySQL due to an extra query after refs #27683.

tests/check_framework/test_database.py

@@ -8,6 +8,8 @@ from django.test import TestCase
 
 
 class DatabaseCheckTests(TestCase):
+    multi_db = True
+
     @property
     def func(self):
         from django.core.checks.database import check_database_backends