[1.8.x] Fixed #24658 -- Added missing Meta attribute in schema tests

Without that, the Note model would be initially created and then
the tests using that model failed when run in isolation.
Backport of f54c0ec06e from master.

tests/schema/models.py

@@ -83,6 +83,9 @@ class BookWithSlug(models.Model):
 class Note(models.Model):
     info = models.TextField()
 
+    class Meta:
+        apps = new_apps
+
 
 class Tag(models.Model):
     title = models.CharField(max_length=255)