test(mesh): host_network direct-path check can see the runner's public endpoint #189

The host_network mesh scenario failed once on a hosted runner at assert_direct_paths, after every other check had passed:

FAIL: grtest-node1 reaches grtest-node3 only indirectly: pong from grtest-node3 (100.64.0.3) via <the runner's public address>:58418 in 0s

The path was direct, but it went to the endpoint Tailscale learnt over STUN (the runner's public address, hairpinned back through its NAT) rather than node 3's daemon address on the test network, which the check requires. node1 to node2 in the same run went over 172.31.250.12. A rerun of the job passed.

Failed run: https://github.com/ExaDev/github-runner/actions/runs/41616497532/job/125851142782 (PR #186, which does not change this scenario).