testing: fix test_upgrade_statickey_onchaind

Seems a timing issue that should be figured out, his makes the test pass.

tests/test_connection.py

@@ -3541,6 +3541,9 @@ def test_upgrade_statickey_onchaind(node_factory, executor, bitcoind):
     l1.daemon.wait_for_log('option_static_remotekey enabled at 1/1')
 
     # Pre-statickey penalty works.
+    # FIXME: Without this sleep, l1 will broadcasts one tx more compared to good
+    # case, causing `wait_for_onchaind_broadcast` to timeout.
+    time.sleep(5)
     bitcoind.rpc.sendrawtransaction(tx)
     bitcoind.generate_block(1)