ci: check if Elixir files are formatted in pre-commit hook

scripts/git-hook-pre-commit.sh

@@ -4,6 +4,9 @@ set -euo pipefail
 
 OPT="${1:--c}"
 
+# mix format check is quite fast
+mix format --check-formatted
+
 files_dirty="$(git diff --name-only | grep -E '.*\.erl' || true)"
 files_cached="$(git diff --cached --name-only | grep -E '.*\.erl' || true)"
 if [[ "${files_dirty}" == '' ]] && [[ "${files_cached}" == '' ]]; then