Update dependency djangorestframework to v3.15.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
djangorestframework (source, changelog)	==3.14.0 -> ==3.15.0

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Release Notes

encode/django-rest-framework (djangorestframework)

### [`v3.15.0`](https://togithub.com/encode/django-rest-framework/compare/3.14.0...3.15.0) [Compare Source](https://togithub.com/encode/django-rest-framework/compare/3.14.0...3.15.0)

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