Fix bug in FsArtifactSource where empty base_uri would cause wrong fsspec fs to be used
Bug: T307115
How to register an account on GitLab. Due to spam, new accounts are locked until approved by an admin or the approver bot. Your GitLab account gets automatically approved within one hour if you are a member of Trusted Contributors in Gerrit, or a member of the Trusted-Contributors group in Phabricator and linked your Developer account ("LDAP") to your Phabricator account. If none of these apply, file an unlock request to expedite access. Only if you are WMF staff: Create your GitLab account, have "Wmf" group membership in IDM, link your Developer account ("LDAP") to your Phabricator account, and get automatically approved.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
Bug: T307115