The recent deployment T294447 has broken Pywikibot imports from Commons, as the script will attempt a copy-upload if it can, but will then fail because the Commons URL isn't in the wgCopyUploadsDomains whitelist.
Previously, this worked because when upload-by-url was disabled, it would download the file to the script's machine and then re-upload.
This domain should be added, as this is a very common use case due to the WS copyright policies vs. Commons.