Running `echo GPP0 >> /proc/acpi/wakeup` into a systemd unit at boot solved the issue for me... except the first sleep after a boot would always wake back up immediately.
I applied your udev rule and that issue seems to be resolved as well!
I remember there being some strange interaction with the wakeup behaviour being toggled otherwise. But this could be due to me being on NixOS.
If you don't add "RemainAfterExit", the service will run at every boot, because after a reboot it is considered "inactive. This will execute your shell code, which effectively toggles wakeup.
"RemainAfterExit" is meant for unit files that change the state of your system. After running once, the service will be considered "active", until you manually deactivate it, which will execute whatever you might have set in "ExecStop".
"Type=Oneshot" is necessary for "RemainAfterExit".
In this case I still would prefer doing it via udev though. I've made it my rule of thumb to evade shell scripting wherever feasible, because it usually ends up being more brittle, and more prone to footgunning :)