deps: update ruff requirement from >=0.15.12 to >=0.15.14 in /backend

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@0.15.12...0.15.14)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.14
  dependency-type: direct:development
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -35,7 +35,7 @@ dependencies = [
 ]
 
 [dependency-groups]
-dev = ["ruff>=0.15.12"]
+dev = ["ruff>=0.15.14"]
 test = [
     "httpx>=0.28.0",
     "nest-asyncio>=1.6.0",