Make local_driver use start_new_session when spawning children

This makes it more in line with lsf driver.
preexec_fn can also deadlock when using fork method for multiprocessing
module.

src/ert/scheduler/local_driver.py

@@ -3,7 +3,6 @@
 import asyncio
 import contextlib
 import logging
-import os
 import signal
 from asyncio.subprocess import Process
 from contextlib import suppress
@@ -106,7 +105,7 @@ async def _init(iens: int, executable: str, /, *args: str) -> Process:
         return await asyncio.create_subprocess_exec(
             executable,
             *args,
-            preexec_fn=os.setpgrp,
+            start_new_session=True,
         )
 
     @staticmethod