Cleanup with ruff check (#963)

* Implement improvements suggested by ruff check.

* Add ruff check to CI.

* Add changelog fragment.

antsibull-nox.toml

@@ -16,6 +16,8 @@ stable_branches = [ "stable-*" ]
 run_isort = true
 isort_config = ".isort.cfg"
 run_black = true
+run_ruff_check = true
+ruff_check_config = "ruff.toml"
 run_flake8 = true
 flake8_config = ".flake8"
 run_pylint = true