ci: bump django from 5.2.13 to 5.2.15

Bumps [django](https://github.com/django/django) from 5.2.13 to 5.2.15.
- [Commits](django/django@5.2.13...5.2.15)

---
updated-dependencies:
- dependency-name: django
  dependency-version: 5.2.15
  dependency-type: direct:production
...

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Author: dependabot[bot]