Docker in docker?

I’d like to do

docker-compose up -d

as part of testing. I understand that it can be done with a trusted repository, but I don’t want to take the risk.

Seems like plugins/docker is able to do what I want, but it fails if I don’t specify the publish-related stuff. I want to use it without publishing.

Another alternative could be services, but I want to avoid maintaining both them and docker-compose.yml.

Since you’re already maintaining a .drone.yml and a docker-compose file, the right way to go is using services, like you suggested.
It shouldn’t be frequently changed assuming you’re separating your services builds correctly.