fix: check stderr output deactivating luks volume

[gabelluardo]

systemd-cryptsetup behaves unexpectedly when trying to unmount a volume that doesn't exist or is already inactive. Even though it fails and prints Device is not active to stderr, it still returns an exit code 0, consequentially the Deactivate function doesn't return an error and the operation is reported as successful by tpmctl.

I’ve updated the check to ensure that if there is any output in stderr, it's treated as an error even if the exit code is 0.