zfsnap does not work under systemd - errors writing to /dev/stderr

[Georgi Georgiev]

This issue is reported upstream at https://github.com/zfsnap/zfsnap/issues/91 and fixed in https://github.com/zfsnap/zfsnap/commit/f895af7835fdc08f7115b31307e71a064e8afe7b

The issue is that when running zfSnap under cron which is managed by systemd-cron we get errors like these and snapshots are not created.

```
$ sudo systemctl status cron-daily-zfSnap.service
○ cron-daily-zfSnap.service - [Cron] /etc/cron.daily/zfSnap
     Loaded: loaded (/etc/cron.daily/zfSnap; generated)
     Active: inactive (dead) since Sat 2024-05-11 01:02:32 JST; 8min ago
TriggeredBy: ● cron-daily-zfSnap.timer
       Docs: man:systemd-crontab-generator(8)
    Process: 57556 ExecStart=/etc/cron.daily/zfSnap (code=exited, status=0/SUCCESS)
   Main PID: 57556 (code=exited, status=0/SUCCESS)
        CPU: 1.144s

May 11 01:02:31 neo systemd[1]: Starting cron-daily-zfSnap.service - [Cron] /etc/cron.daily/zfSnap...
May 11 01:02:31 neo zfSnap[57557]: /usr/sbin/zfSnap: 365: cannot create /dev/stderr: No such device or address
May 11 01:02:31 neo zfSnap[57557]: /usr/sbin/zfSnap: 365: cannot create /dev/stderr: No such device or address
May 11 01:02:32 neo systemd[1]: cron-daily-zfSnap.service: Deactivated successfully.
May 11 01:02:32 neo systemd[1]: Finished cron-daily-zfSnap.service - [Cron] /etc/cron.daily/zfSnap.
May 11 01:02:32 neo systemd[1]: cron-daily-zfSnap.service: Consumed 1.144s CPU time.
May 11 01:02:32 neo systemd[1]: cron-daily-zfSnap.service: Triggering OnSuccess= dependencies.
```

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: zfsnap 1.11.1-8.1
Uname: Linux 5.15.146.1-microsoft-standard-WSL2 x86_64
ApportVersion: 2.28.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: unknown
CloudArchitecture: x86_64
CloudBuildName: server
CloudID: none
CloudName: none
CloudPlatform: none
CloudSerial: 20190521
CloudSubPlatform: config
Date: Sat May 11 01:05:09 2024
PackageArchitecture: all
ProcEnviron:
 LANG=C.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=tmux-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: zfsnap
UpgradeStatus: Upgraded to noble on 2024-05-09 (1 days ago)