Modify the `OsBuildJob` implementation to handle multiple upload targets
in a cycle. However, there is still no API implementation, which would be
adding `OsBuildJobs` with multiple targets to the job queue.
The limitations are that only a single osbuild export is supported, and
the same artifact will be used for each target.
At the end of the job, errors from all targets are gathered. In case
there are none, the job succeeds. In case at least one target failed,
the job fails as well. In such a case, a slice of errors from all failed
targets is added to the job error as details.
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