Bump ruff from 0.5.5 to 0.5.6 (#438)

requirements_testing.txt

@@ -4,7 +4,7 @@ pylint==3.2.6
 pytest==8.3.2
 pytest-cov==5.0.0
 pytest-icdiff==0.9
-ruff==0.5.5
+ruff==0.5.6
 setuptools==72.1.0
 tox==4.16.0
 tox-gh-actions==3.2.0