`AttributeError: 'Loop' object has no attribute 'fd'` about bootc-image-builder

[mvo5]

One (small) step forward with this should be osbuild/osbuild#1467 to ensure we get correct error reporting from open(). The underlying issue is in the stracktrace:

   File "/usr/lib/python3.12/site-packages/osbuild/host.py", line 384,
in call_with_fds
     raise error
osbuild.host.RemoteError: FileNotFoundError: [Errno 2] No such file or
directory: 'loop1'

but that is hidden from the top because of the incorrect cleanup in del.

Sorry if I'm stating the obvious here but I wanted to spell it out as it was not obvious at first to me.