Remove unnecessary type conversions

[franciscouzo]

Since 3.5, it's possible to merge dictionaries with the ** syntax.
When Python 3.9 is the minimum supported version (2024), we'll be able to do validated_data = self.validated_data | kwargs .

[lovelydinosaur]

These look neater, yup. Thank you!

[jgrewal1991]

@tomchristie @franciscouzo
After this change, look like formData posted is getting little messed up. In my case, validated_data in previous versions was coming up as :
{'name': '2020.pdf', 'type': 1, 'creator': 'asdfga69-cdgaba-46e5-bfdge-da2fgdsfac77', 'additional_data': {'designation': 2, 'date': '2020-11-01', 'number': 'dafsda'}}

but now, it is becoming:

{'name': ['2020.pdf'], 'type': [1], 'creator': ['asdfga69-cdgaba-46e5-bfdge-da2fgdsfac77'], 'additional_data': [{'designation': 2, 'date': '2020-11-01', 'number': 'dafsda'}]}

Due to which validations are failing.
https://github.com/encode/django-rest-framework/pull/7526/files#diff-c33f1f011c9f5cf3ed1357b809ebf2b4ed0b808b227c6c007291bf9b259422ecR197

[carltongibson]

@jgrewal1991 Can you open a new issue with this please? Ideally if you could provide a test case that demonstrates the regression that would help. Thanks.

[jgrewal1991]

@carltongibson #7623