fix: set Docker network for WP CI step containers

CI step containers spawned by the WP agent (running on host network)
cannot resolve Docker service names like forgejo. Setting
WOODPECKER_BACKEND_DOCKER_NETWORK puts CI containers on the compose
network so they can reach Forgejo for git clone.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bin/disinto

@@ -214,6 +214,7 @@ services:
       WOODPECKER_AGENT_SECRET: ${WOODPECKER_AGENT_SECRET:-}
       WOODPECKER_GRPC_SECURE: "false"
       WOODPECKER_HEALTHCHECK_ADDR: ":3333"
+      WOODPECKER_BACKEND_DOCKER_NETWORK: disinto_disinto-net
       WOODPECKER_MAX_WORKFLOWS: 1
     depends_on:
       - woodpecker