When checking for new images on registries, do not suppress
and debug-log errors but return them. Other images and units
will still be processed.
That is important to a) stop hiding flaky registries (see #18321)
b) mark the updates as `failed` instead of `false`
[NO NEW TESTS NEEDED]
Closes: #18321
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>