Unfortunately it is not possible to take advantage of the SAN workaround with Caddy. 
Since you appear to be standing up a new service and not migrating an existing one to HTTPS, if you don’t want to wait a week or switch away from Caddy you could use a different subdomain like ci.dirtydevelopers.org instead.
P.S. if you know you’re going to have to redo things a couple times it’s a good idea to use the staging server. It doesn’t give you real certificates so you’ll have to bypass certificate warnings during testing but it has it’s own, much higher, rate limits so you can test things without worries.
caddy -ca https://acme-staging.api.letsencrypt.org/directory
or add this to your Caddyfile:
tls <email> {
ca https://acme-staging.api.letsencrypt.org/directory
}