fall back to system ruff executable without executable setting

Author: TheJJ

pylsp_ruff/plugin.py

@@ -3,6 +3,7 @@
 import logging
 import re
 import sys
+import shutil
 from pathlib import PurePath
 from subprocess import PIPE, Popen
 from typing import Dict, Generator, List, Optional
@@ -518,7 +519,7 @@ def run_ruff(
     String containing the result in json format.
 
     """
-    executable = settings.executable
+    executable = settings.executable or shutil.which("ruff")
 
     arguments = subcommand.build_args(document_path, settings, fix, extra_arguments)