As the name already suggests, the Sagan ruleset is not for Suricata, but for Sagan (GitHub - quadrantsec/sagan: Sagan is a multi-threads, high performance log analysis engine. At it's core, Sagan similar to Suricata/Snort but with logs rather than network packets.) which is a different tool with a different purpose.
While the rule format might be similar to Suricata’s, the keywords are different. Its rules will not work with Suricata.