test: Adjust expected systemd message for scheduled reboot
test: Adjust expected systemd message for scheduled reboot

Latest systemd fixes the message for a scheduled reboot to actually say
"Reboot" instead of "Shutdown". Accept either.

Closes #14438

moraleslazaro/cockpit,mvollmer/cockpit,garrett/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,deryni/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,garrett/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,deryni/cockpit