django 4 support: Add missing dependency for memcache
This adapts the memcached import the same way the swh.web module did. Follow up 9210c012 Refs. swh/infra/sysadm-environment#5129
This adapts the memcached import the same way the swh.web module did. Follow up 9210c012 Refs. swh/infra/sysadm-environment#5129