fix: offline iso update

[bobslept]

Fixes #86

This will always return True when we are on a offline installation which contains the oci variant oci:/var/ublue-os/image

Add another condition to verify we want to have a dbus notification

Traceback (most recent call last):
  File "/usr/bin/ublue-update", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/lib/python3.11/site-packages/ublue_update/cli.py", line 255, in main
    run_updates(cli_args.system, system_update_available)
  File "/usr/lib/python3.11/site-packages/ublue_update/cli.py", line 177, in run_updates
    if "universal-blue-update-reboot" in out.stdout.decode("utf-8"):
                                         ^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'stdout'

Bump the spec version with x.x.1