Fixed #28653 -- Added missing ForeignKey.on_delete argument in docs.

docs/topics/db/aggregation.txt

@@ -34,7 +34,7 @@ used to track the inventory for a series of online bookstores:
         price = models.DecimalField(max_digits=10, decimal_places=2)
         rating = models.FloatField()
         authors = models.ManyToManyField(Author)
-        publisher = models.ForeignKey(Publisher)
+        publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE)
         pubdate = models.DateField()
 
     class Store(models.Model):

docs/topics/db/queries.txt

@@ -34,7 +34,7 @@ models, which comprise a Weblog application:
             return self.name
 
     class Entry(models.Model):
-        blog = models.ForeignKey(Blog)
+        blog = models.ForeignKey(Blog, on_delete=models.CASCADE)
         headline = models.CharField(max_length=255)
         body_text = models.TextField()
         pub_date = models.DateField()