QA works poorly for uploads without an orig tarball

In https://debusine.debian.net/debian/developers/work-request/73938/, I made a test upload of a fairly typical 3.0 (quilt) package using my dput-ng integration branch. Since the Debian revision wasn't 1, the upload didn't include the .orig.tar.gz. The sbuild tasks worked fine, because the sbuild workflow looks up the appropriate debian:source-package artifact when constructing its task data, and that includes the orig tarball. However, the autopkgtest tasks failed, because the autopkgtest workflow just passes through the debian:upload artifact, which in this case does not include the orig tarball. More subtly, the lintian tasks succeeded, but on closer inspection they just skipped the source package because it was incomplete, for the same reason.

I think we should just be able to run input.source_artifact through workflow_utils.locate_debian_source_package_lookup in the autopkgtest and lintian workflows, the same way we do for sbuild.