ci: stop waiting ~9 minutes on an unreachable cache

Validate took ~10 minutes, of which ~10 seconds was work: setup-go's
cache restore and save each waited ~4.7 minutes for a connect timeout,
because the runners' built-in cache server sits on a network job
containers can't reach. Turn off setup-go caching (three small modules
aren't worth it) and the game-test runner's cache server, so any cache
step skips at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/runner/config.yaml

@@ -3,6 +3,11 @@ runner:
   capacity: 1
   timeout: 3h
 
+cache:
+  # The built-in cache server listens on the runner container's own network, which job containers
+  # can't reach: every cache restore/save waited ~4.7 minutes for a timeout. Off, they skip at once.
+  enabled: false
+
 container:
   # Empty = use the host's Docker and mount it into job containers, which the boot test needs
   # to start the node-agent and game containers