pytest: fix flake in test_listforwards_and_listhtlcs

Make sure l1 sees chanell to l4.

```
   def test_listforwards_and_listhtlcs(node_factory, bitcoind):
        """Test listforwards and listhtlcs commands."""
        l1, l2, l3, l4 = node_factory.get_nodes(4, opts=[{}, {}, {}, {}])
    
        l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
        l2.rpc.connect(l3.info['id'], 'localhost', l3.port)
        l2.rpc.connect(l4.info['id'], 'localhost', l4.port)
    
        c12, c12res = l1.fundchannel(l2, 10**5)
        c23, _ = l2.fundchannel(l3, 10**5)
        c24, _ = l2.fundchannel(l4, 10**5)
    
        # Wait until channels are active
        mine_funding_to_announce(bitcoind, [l1, l2, l3, l4])
        l1.wait_channel_active(c23)
    
        # successful payments
        i31 = l3.rpc.invoice(1000, 'i31', 'desc')
        l1.rpc.pay(i31['bolt11'])
    
        i41 = l4.rpc.invoice(2000, 'i41', 'desc')
>       l1.rpc.pay(i41['bolt11'])

tests/test_misc.py:2871: 
...
>           raise RpcError(method, payload, resp['error'])
E           pyln.client.lightning.RpcError: RPC call failed: method: pay, payload: {'bolt11': 'lnert20n1pjnd7xlsp5lcwwuxw90nanl7cpfzp4jf7w5tats5aalkksswpps6cqrwpu0l3spp5pzng94efstxjhdc2ya8hhgrch33qavzgv4gahga3y6dxqshezuqsdq8v3jhxccxqyjw5qcqp99qxpqysgqys70jhf8aj4zpwrvfrse54c5kfaqxj98xl4ddxp7jkm75e4p59gy6l2ryvz4fejg5reqkxw44k90rp0l7c8vxut424m4ek743k0lpwcqzg2a60'}, error: {'code': 210, 'message': 'Destination 0382ce59ebf18be7d84677c2e35f23294b9992ceca95491fcf8a56c6cb2d9de199 is not reachable directly and all routehints were unusable.', 'attempts': [{'status': 'failed', 'failreason': 'Destination 0382ce59ebf18be7d84677c2e35f23294b9992ceca95491fcf8a56c6cb2d9de199 is not reachable directly and all routehints were unusable.', 'partid': 0, 'amount_msat': 2000msat}]}
```

Signed-off-by: Rusty Russell <[email protected]>

tests/test_misc.py

@@ -2862,6 +2862,7 @@ def test_listforwards_and_listhtlcs(node_factory, bitcoind):
     # Wait until channels are active
     mine_funding_to_announce(bitcoind, [l1, l2, l3, l4])
     l1.wait_channel_active(c23)
+    l1.wait_channel_active(c24)
 
     # successful payments
     i31 = l3.rpc.invoice(1000, 'i31', 'desc')