Move signal disconnect into finally block

        def log_post_delete(instance, **kwargs):

            self.assertTrue(R.objects.filter(pk=instance.r_id))

        models.signals.post_delete.connect(log_post_delete, sender=S)

        r = R.objects.create(pk=1)

        S.objects.create(pk=1, r=r)

        r.delete()

        models.signals.post_delete.connect(log_post_delete, sender=S)

        try:

            r.delete()

        finally:

            models.signals.post_delete.disconnect(log_post_delete)

    @skipUnlessDBFeature("can_defer_constraint_checks")