Please keep in mind that your Drone server is probably running in a container attached to the default bridge network. However, when Drone spawns pipeline containers it creates a user-defined network, and the clone happens inside that user-defined network, not the default bridge network.
The dns used by user-defined networks in Docker is different than the dns used by bridge networks. This means the nslookup test you ran is not really an accurate test, since it is testing the bridge network, as opposed to a user-defined network.
There are some existing threads you can read that include suggestions for testing user-defined networks on your machine. Here are a few threads that I recommend: