No systemd notification when user suspend system by sleepgraph

Hello,

sleepgraph utilize sysfs node to suspend the system, ex: $ echo mem > /sys/power/state. Some devices customize the pre-sleep or post-resume operations by utilizing systemd sleep script, ex: Nvidia proprietary driver. It may cause some problem on the device that needs pre-sleep or post-resume operations.

Reproduce steps:

On Ubuntu 22.04 system with NV graphic

1. install nvidia driver by $ sudo ubuntu-drivers install nvidia:535
2. Suspend the system by $ sleepgraph -m freeze -rtcwake 60 -sync -gzip -multi 1 0 -skiphtml
3. The nvidia-sleep.sh won't be triggered

Thanks,