fuuko/drone/runner-exec: Remove port collision with grafana

Drone docs [1] say “Overriding this value is not recommended”, however I
do not see why I should not be able to change it.

[1] https://docs.drone.io/runner/exec/configuration/reference/drone-http-bind/

machines/fuuko/services/drone/runner-exec.nix

@@ -24,6 +24,7 @@ in
     };
     path = availablePkgs;
     environment = {
+      DRONE_HTTP_BIND = ":3002";
       DRONE_RPC_HOST = "ci.sbruder.de";
       DRONE_RPC_PROTO = "https";
       DRONE_RUNNER_CAPACITY = "2";