Bump ruff from 0.15.5 to 0.15.6 in /requirements

Bumps [ruff](https://github.com/astral-sh/ruff) from 0.15.5 to 0.15.6.
- [Release notes](https://github.com/astral-sh/ruff/releases)
- [Changelog](https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md)
- [Commits](astral-sh/ruff@0.15.5...0.15.6)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

requirements/test.txt

@@ -3,5 +3,5 @@ packaging==26.0
 pytest==9.0.2
 pytest-xdist==3.8.0
 pytest-cov==7.0.0
-ruff==0.15.5
+ruff==0.15.6
 setuptools==82.0.1