private/deposit_checks: Ensure checks is done on filename
If done on the full path, the conditional technically fails the check for the wrong reason. This also adds tests on this case. Refs. swh/infra/sysadm-environment#5129
If done on the full path, the conditional technically fails the check for the wrong reason. This also adds tests on this case. Refs. swh/infra/sysadm-environment#5129