dovecot: fixed sa-rules download #519

Job	Run time
docker_image_builds (acme-mailcow)	52s
docker_image_builds (clamd-mailcow)	51s
docker_image_builds (dockerapi-mailcow)	1m 1s
docker_image_builds (dovecot-mailcow)	1m 7s
docker_image_builds (netfilter-mailcow)	58s
docker_image_builds (olefy-mailcow)	1m 5s
docker_image_builds (php-fpm-mailcow)	1m 23s
docker_image_builds (postfix-mailcow)	1m 9s
docker_image_builds (rspamd-mailcow)	1m 1s
docker_image_builds (sogo-mailcow)	1m 11s
docker_image_builds (solr-mailcow)	1m 1s
docker_image_builds (unbound-mailcow)	51s
docker_image_builds (watchdog-mailcow)	45s
	13m 15s

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