Primary key of m2m tables is not migrated to BigAutoField

[Jeremy Lainé]

I am trying to upgrade an existing application's models to use only "bigint" primary keys on postgresql. To do this I changed DEFAULT_AUTO_FIELD to BigAutoField, generated the migrations then applied them.

The tables for my explicitly defined models get upgraded correctly. The many-to-many intermediate tables on the other hand still have an "integer" primary key, with the 32bit limit I'm trying to avoid.

The following model are sufficient to reproduce the issue:

`
class Book(models.Model):

name = models.CharField(max_length=255)
tags = models.ManyToManyField("Tag")

class Tag(models.Model):

name = models.CharField(max_length=255)

`

The resulting schema for the testapp_book_tags looks like:

`
test=> \d testapp_book_tags;

Table "public.testapp_book_tags"

Column | Type | Collation | Nullable | Default

---

id | integer | | not null | nextval('testapp_book_tags_id_seq'::regclass)
book_id | bigint | | not null |
tag_id | bigint | | not null |

`