tests: flaky test_gossip_pruning timeouts while waiting for channel announce

[daywalker90]

The test in test_gossip.py seems to fail in the CI sometimes.

It timeouts on this line:

wait_for(lambda: [c['active'] for c in l3.rpc.listchannels()['channels']] == [True] * 4)

And i noticed this in the logs:

lightningd-3 2024-04-17T13:39:35.951Z DEBUG   plugin-topology: Note: disallowing deprecated listchannels.include_private for \"-c:listchannels#84/cln:listchannels#404\"
lightningd-3 2024-04-17T13:39:38.669Z DEBUG   022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59-gossipd: seeker: state = ASKING_FOR_UNKNOWN_SCIDS Asking for 1 scids
lightningd-3 2024-04-17T13:39:38.670Z DEBUG   022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59-gossipd: sending query for 1 scids
[...]
lightningd-3 2024-04-17T13:39:38.682Z UNUSUAL lightningd: Bad gossip order: could not find channel 103x1x0 for peer's channel update