I have a Django model that used to look like this:class Car(models.Model): manufacturer_id = models.IntegerField()There is another model called Manufacturer that the id field refers to. However, I realized that it would be useful to use Django's built-in foreign key functionality, so I changed the model to this:class Car(models.Model): manufacturer = models.ForeignKey(Manufacturer)This change appears to work fine immediately, queries work without errors, but when I try to run migrations, ...