tests: don't run migrations if environment has DISABLE_MIGRATIONS (#12889)

tests/settings.py

@@ -22,3 +22,13 @@ TEMPLATE_VARS = {}
 
 import tempfile
 MEDIA_ROOT = tempfile.mkdtemp('combo-test')
+
+if 'DISABLE_MIGRATIONS' in os.environ:
+    class DisableMigrations(object):
+        def __contains__(self, item):
+            return True
+
+        def __getitem__(self, item):
+            return 'notmigrations'
+
+    MIGRATION_MODULES = DisableMigrations()