pytest: fix flake in tests/test_bookkeeper.py::test_bookkeeping_missed_chans_leases

```
 FAILED tests/test_bookkeeper.py::test_bookkeeping_missed_chans_leases - AssertionError: assert [{'tag': 'channel_open', 'credit_msat': 506268000, 'debit_msat': 0}, {'tag': 'lease_fee', 'credit_msat': 0, 'debit_msat': 6268000}, {'tag': 'invoice', 'credit_msat': 0, 'debit_msat': 11000000}, {'tag': 'onchain_fee', 'credit_msat': 1314000, 'debit_msat': 0}] == [{'tag': 'channel_open', 'credit_msat': 506268000, 'debit_msat': 0}, {'tag': 'lease_fee', 'credit_msat': 0, 'debit_msat': 6268000}, {'tag': 'onchain_fee', 'credit_msat': 1314000, 'debit_msat': 0}, {'tag': 'invoice', 'credit_msat': 0, 'debit_msat': 11000000}]
  
  At index 2 diff: {'tag': 'invoice', 'credit_msat': 0, 'debit_msat': 11000000} != {'tag': 'onchain_fee', 'credit_msat': 1314000, 'debit_msat': 0}
  
  Full diff:
    [
        {
            'credit_msat': 506268000,
            'debit_msat': 0,
            'tag': 'channel_open',
        },
        {
            'credit_msat': 0,
            'debit_msat': 6268000,
            'tag': 'lease_fee',
        },
        {
  +         'credit_msat': 0,
  +         'debit_msat': 11000000,
  +         'tag': 'invoice',
  +     },
  +     {
            'credit_msat': 1314000,
            'debit_msat': 0,
            'tag': 'onchain_fee',
        },
  -     {
  -         'credit_msat': 0,
  -         'debit_msat': 11000000,
  -         'tag': 'invoice',
  -     },
    ]
```

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

Author: rustyrussell

tests/test_bookkeeper.py

@@ -379,8 +379,14 @@ def test_bookkeeping_missed_chans_leases(node_factory, bitcoind):
     l1.wait_local_channel_active(scid)
     channel_id = first_channel_id(l1, l2)
 
+    # Sigh.  bookkeeper sorts events by timestamp.  If the invoice event happens
+    # too close, it can change the order, so sleep here.
+    time.sleep(1)
+
+    # Send l2 funds via the channel
     l1.pay(l2, invoice_msat)
-    l1.daemon.wait_for_log(r'coin movement:.*\'invoice\'')
+    # Make sure they're completely settled, so accounting correct.
+    wait_for(lambda: only_one(l1.rpc.listpeerchannels()['channels'])['htlcs'] == [])
 
     # Now turn the bookkeeper on and restart
     l1.stop()