Job containers were pinned to a single shared `gitea-actions` bridge
network, added with the Actions cache to give service containers DNS and a
fixed gateway for the built-in cache server. Because every job of every run
attached to that one network, concurrent jobs' service containers collided
on hostnames: two simultaneous jobs that both expose a `redis` service meant
either could resolve the other's container, causing intermittent cross-job
CI failures that vanished when runs did not overlap.
Set `container.network` back to empty so the runner auto-creates an isolated
user-defined network per job. Embedded DNS still works on each per-job
network, so service containers remain reachable by name, but jobs can no
longer resolve each other's containers.
`cache.host` is left empty for auto-detection; the runner here is a host
binary (systemd), not containerized, so the detected address is reachable
from job containers. The cache port stays fixed per runner. The cache
firewall rule now allows Docker's default address pool (172.16.0.0/12)
because per-job subnets are dynamic, and the now-unused `gitea-actions`
network is removed on converge once idle.
raucao