ruff: fail check on reformat

Ensures that CI fails if reformatting is required.

Author: WhyNotHugo

tox.ini

@@ -65,7 +65,7 @@ allowlist_externals = make
 # See: https://github.com/astral-sh/ruff/issues/14698
 deps = ruff!=0.8.1
 commands =
-  ruff format .
+  ruff format --exit-non-zero-on-format .
   ruff check --force-exclude --fix --exit-non-zero-on-fix
 skip_install = true