Using sort_keys kwarg no longer possible with YAML serializer

[Jacob Walls]

The YAML serializer takes a sort_keys option, but since we neglected to use setdefault when "defaulting" this argument in 7142667340f78403cbbcaa8f33703c494282b7b7, any existing uses could raise TypeError:

Test case for YamlSerializerTestCase:

    def test_explicit_sort_keys(self):
        serial_str = serializers.serialize(
            "yaml", Author.objects.all(), sort_keys=False
        )
        self.assertTrue(self._validate_output(serial_str))

  File "/Users/jwalls/django/tests/serializers/test_yaml.py", line 159, in test_explicit_sort_keys
    serial_str = serializers.serialize("yaml", Author.objects.all(), sort_keys=False)
    ^^^^^^^^^^^^^^^
  File "/Users/jwalls/django/django/core/serializers/__init__.py", line 134, in serialize
    s.serialize(queryset, **options)
      ^^^^^^^^^^^^^^^^^
  File "/Users/jwalls/django/django/core/serializers/base.py", line 149, in serialize
    self.end_serialization()
    ^^^^^^^^^^^^^^^
  File "/Users/jwalls/django/django/core/serializers/pyyaml.py", line 49, in end_serialization
    yaml.dump(
TypeError: yaml.dump() got multiple values for keyword argument 'sort_keys'

[Jacob Walls]

​PR