В дефолтном конфиге раннера указана сеть gitea_network

runner/config.example.yaml

@@ -64,7 +64,7 @@ container:
   # Specifies the network to which the container will connect.
   # Could be host, bridge or the name of a custom network.
   # If it's empty, act_runner will create a network automatically.
-  network: ""
+  network: "gitea_network"
   # Whether to use privileged mode or not when launching task containers (privileged mode is required for Docker-in-Docker).
   privileged: false
   # And other options to be used when the container is started (eg, --add-host=my.gitea.url:host-gateway).