Package `update_from_scan` is not triggered from already existing scans

[tdruez]

From https://github.com/nexB/dejacode/issues/26#issuecomment-1879020960

one other observation, which is not directly related to this issue, but something that is somewhat perplexing. DejaCode found the existing scans that I created yesterday for the 4 packages (good) and apparently they did not get re-scanned (fine I think) but it did not perform any of the auto-updates to fields on the package (not so good), such as the license-expression, even though 3 of the 4 scans have a declared license. See attached.

Note that this is not urgent as this is not a usual use case as it's more a side effect of a testing behavior (removing and re-adding already scanned packages)