chore(deps): update ruff requirement from ~=0.6.7 to ~=0.6.8

Updates the requirements on [ruff](https://github.com/astral-sh/ruff) to permit the latest version.
- [Release notes](https://github.com/astral-sh/ruff/releases)
- [Changelog](https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md)
- [Commits](astral-sh/ruff@0.6.7...0.6.8)

---
updated-dependencies:
- dependency-name: ruff
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/requirements.txt

@@ -10,5 +10,5 @@ python-dotenv~=1.0.1
 gunicorn~=23.0.0
 djangorestframework~=3.15.2
 pytest-django~=4.9.0
-ruff~=0.6.7
+ruff~=0.6.8
 pydantic~=2.9.2