Revert container network to bridge mode

Host network breaks DinD connection. Bridge with --mtu=1340
is confirmed working for TLS connections.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gitea-runner/deployment.yaml

@@ -25,7 +25,7 @@ data:
         - "ubuntu-22.04:docker://catthehacker/ubuntu:act-22.04"
         - "self-hosted:host"
     container:
-      network: "host"
+      network: ""
       privileged: false
       options:
       valid_volumes: []