trivial: fwupd-refresh: allow exit code 2 for success
trivial: fwupd-refresh: allow exit code 2 for success

This is no supported devices, and shouldn't cause systemd failures
for fwupd-refresh.

fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd