Update service fails on offline iso install

[bobslept]

It wants to read contents from rpm-ostree status --json but can't be used the same way as a "normal" installation. I've tested on rpm-ostree rebase ostree-unverified-registry:ghcr.io/ublue-os/bluefin:38 install and that works great.

The offline install errors out with the following message:

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 235, in main
    system_update_available: bool = system_update_check()
                                    ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/ublue_update/update_checks/system.py", line 43, in system_update_check
    latest_digest = skopeo_inspect(url)
                    ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/ublue_update/update_checks/system.py", line 15, in skopeo_inspect
    digest = loads(inspect)["Digest"]
             ^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Based on the code, it seems to read contents from rpm-ostree status --json so I will provide a dump from that too:
https://paste.centos.org/view/175f56cd