Fixed #13711 -- Model check added to ensure that auto-generated field name is within limits of the database.

...ion.
these lines are a bit long...
```
m2m_field = models.ManyToManyField(
    VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
    related_name="rn1",
)
```