rule_config.yml.j2: Send warn alerts to team-X-mails-regular

We were temporarily sending warn alerts to team-X-mails-urgent due
to the following issue -> scylladb/scylla-monitoring#2101.
Now that this issue has been fixed we can send these alerts to
team-X-mails-regular.

ansible-scylla-monitoring/templates/rule_config.yml.j2

@@ -71,7 +71,7 @@ route:
   routes:
   - match:
       severity: "warn"
-    receiver: team-X-mails-urgent
+    receiver: team-X-mails-regular
   - match:
       severity: "error"
     receiver: team-X-mails-urgent