Update ruff requirement from >=0.5.5 to >=0.15.12

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@0.5.5...0.15.12)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.12
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -4,7 +4,7 @@ pytest-cov
 pytest-mockito
 robotstatuschecker
 black >= 25.11.0
-ruff >= 0.5.5
+ruff >= 0.15.12
 robotframework-tidy
 invoke >= 3.0.3
 twine