Investigate the ContentDisallowed exception

There seem to be trouble in the celery/rabbitmq communication with [1]

This impacts all modules using celery/rabbitmq (loader, lister, vault, ...) [2]. It does not seem to prevent the overall stack from running though.

• [1] https://sentry.softwareheritage.org/share/issue/b3632f4f2c5c4f9a926f36c1fce4a906/

• [2] sentry says at least 3k for each dvcs loaders and lister, 27k for the loader-core...

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Migrated from T3632 (view on Phabricator)