Randomly getting "setpgid: Permission denied"

I am getting this error about once a day with simple commands like `ls` or running a python script and I cannot reproduce it manually. Seems to originate from [shell/job.c:42](https://git.sr.ht/~emersion/mrsh/tree/master/item/shell/job.c#L42). There was a similar issue in [fish-shell](https://github.com/fish-shell/fish-shell/issues/4715) and they silenced the error.

Start at shell/job.c:42 and compare the reported setpgid behavior with the linked fish-shell issue. Reproduce or investigate the intermittent error using simple commands such as ls or a Python script, then verify that the completed change prevents the unwanted error without disrupting job handling.

Written by the indexing model from the issue text.