CI: Omit file list in Ruff check (MR 35)

Ruff will recursively lint all files in subdirectories if no list of
files is omitted. This also lets us remove the ShellCheck ignore as the
affected code no longer exist.

[ci:skip-build]: already built successfully in CI

.ci/ruff.sh

@@ -10,6 +10,5 @@ fi
 
 set -x
 
-# shellcheck disable=SC2046
-ruff check $(find .ci -name '*.py')
+ruff check
 ruff format --diff