Inhibit sleep from systemd service

[Gordon Messmer]

I'd like to inhibit suspend while backups run on my laptop.  I'm 
scheduling those backups with a systemd timer[1] and service[2]. I've 
read that the default polkit policy only permits inhibiting suspend from 
within a login session, so I've also tried to add rules to allow the 
root user to inhibit suspend[3].  However, with all of those in place, I 
still get errors that I think indicate that the "systemd-inhibit" 
command is failing[4].

I'm running this on Fedora 33.  Has anyone successfully used 
systemd-inhibit from a systemd unit?

1:
# cat /usr/lib/systemd/system/run-borg.timer

[Unit]
Description=Periodic borg backup

[Timer]
OnCalendar=08..20/2:00
Persistent=true

[Install]
WantedBy=timers.target

2:
# cat /usr/lib/systemd/system/run-borg.service
[Unit]
Description=Run borg backup
RequiresMountsFor=/var/log
ConditionACPower=true

[Service]
Type=oneshot
ExecStart=/usr/bin/systemd-inhibit --who=borg-backup '--why=Backup in 
progress' --mode=block /root/run-borg

3:
# cat /etc/polkit-1/rules.d/root-inhibit-suspend.rules
polkit.addRule(function(action, subject) {
     if (action.id == "org.freedesktop.login1.inhibit-block-shutdown" &&
         subject.isInGroup("root")) {
         return polkit.Result.YES;
     }
});

polkit.addRule(function(action, subject) {
     if (action.id == "org.freedesktop.login1.inhibit-block-sleep" &&
         subject.isInGroup("root")) {
         return polkit.Result.YES;
     }
});

polkit.addRule(function(action, subject) {
     if (action.id == "org.freedesktop.login1.inhibit-block-idle" &&
         subject.isInGroup("root")) {
         return polkit.Result.YES;
     }
});

4:
Mar 21 18:00:41 vagabond systemd[1]: Starting Run borg backup...
Mar 21 18:00:41 vagabond systemd-inhibit[19767]: read: Connection reset 
by peer
Mar 21 18:00:41 vagabond systemd-inhibit[19761]: /root/run-borg failed 
with exit status 1.
Mar 21 18:00:41 vagabond systemd[1]: run-borg.service: Main process 
exited, code=exited, status=1/FAILURE
Mar 21 18:00:41 vagabond systemd[1]: run-borg.service: Failed with 
result 'exit-code'.
Mar 21 18:00:41 vagabond systemd[1]: Failed to start Run borg backup.