[[ https://sentry.softwareheritage.org/share/issue/12bf8f4461dd4e1cb32d46933b143901/ | committer=None happens on some malformed commits generated by old dgit version ]];
and it is possible for author=None to happen for the same reason.
For now, this is not supported by swh-model, so tests temporarily
disable attrs checks that swh-model relies on.