Add test_directory_add_raw_manifest__different_entries
This reproduces what I think is the issue found in https://jenkins.softwareheritage.org/job/debian/job/packages/job/DSTO/job/gbp-buildpackage/423/consoleFull
This does not fix the issue as it is a consequence of the design, but documents this problematic behavior.
Migrated from D8180 (view on Phabricator)