Checklist

• [✔️] I have verified that that issue exists against the master branch of Django REST framework.
• [✔️] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• [✔️] This is not a usage question. (Those should be directed to the discussion group instead.)
• [✔️] This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• [✔️] I have reduced the issue to the simplest possible case.
• [✔️] I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

ModelSerializer.create() does not work for models with custom managers, in case if there is no model.objects manager.
Small failing example:

class Model(models.Model):
    name = models.CharField(max_length=64)
    all_objects = models.Manager()

class TestModelSerializer(serializers.ModelSerializer):
            class Meta:
                model = Model
                fields = ('name',)

TestModelSerializer().create({'name': 'test_name'})

Expected behavior

Object should be created, either using default managers create(), or just by creating model instance and saving it.

Actual behavior

Exception is raised:

rest_framework/serializers.py:940: in create
    instance = ModelClass.objects.create(**validated_data)
E   AttributeError: type object 'IssueNewTestModel' has no attribute 'objects'