improve celery log during imports

looking at the log, is really not very clear when it started importing a package and why.

Aug 23 23:05:33 wv-debian-mentors1 celery[1121]: [2022-08-23 23:05:33,095: INFO/Beat] Scheduler: Sending due task importer (debexpo.importer.tasks.importer)
Aug 23 23:05:33 wv-debian-mentors1 celery[524]: [2022-08-23 23:05:33,098: INFO/MainProcess] Received task: debexpo.importer.tasks.importer[f0d330ec-73c2-423a-a537-d85eca4ef8bb]
Aug 23 23:05:35 wv-debian-mentors1 celery[1120]: [2022-08-23 23:05:35,989: INFO/ForkPoolWorker-3] POST https://bugs.debian.org/cgi-bin/soap.cgi
Aug 23 23:06:00 wv-debian-mentors1 celery[1120]: Failed to import swift: Source package is invalid
Aug 23 23:06:00 wv-debian-mentors1 celery[1120]: Failed to parse debian/copyright: Files paragraph missing License field
Aug 23 23:06:00 wv-debian-mentors1 celery[1120]: [2022-08-23 23:06:00,703: ERROR/ForkPoolWorker-3] Failed to import swift: Source package is invalid
Aug 23 23:06:00 wv-debian-mentors1 celery[1120]: Failed to parse debian/copyright: Files paragraph missing License field
Aug 23 23:06:04 wv-debian-mentors1 celery[1120]: [2022-08-23 23:06:04,021: INFO/ForkPoolWorker-3] Task debexpo.importer.tasks.importer[f0d330ec-73c2-423a-a537-d85eca4ef8bb] succeeded in 30.92165717900206>

the package name and version should really be mentioned first of all, and I would have expected to see a clear message stating that the package was eventually rejected.