pytest: fix flake in test_wss_proxy

```
>       wss = BindWebSecureSocket('localhost', wss_port)

tests/test_connection.py:4584: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tests/test_connection.py:4570: in __init__
    self.ws.connect("wss://" + hostname + ":" + str(port))
../../../.cache/pypoetry/virtualenvs/cln-meta-project-AqJ9wMix-py3.8/lib/python3.8/site-packages/websocket/_core.py:256: in connect
    self.sock, addrs = connect(
../../../.cache/pypoetry/virtualenvs/cln-meta-project-AqJ9wMix-py3.8/lib/python3.8/site-packages/websocket/_http.py:145: in connect
    sock = _open_socket(addrinfo_list, options.sockopt, options.timeout)
../../../.cache/pypoetry/virtualenvs/cln-meta-project-AqJ9wMix-py3.8/lib/python3.8/site-packages/websocket/_http.py:232: in _open_socket
    raise err
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

addrinfo_list = [(<AddressFamily.AF_INET6: 10>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('::1', 45521, 0, 0)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('127.0.0.1', 45521))]
sockopt = [], timeout = None

    def _open_socket(addrinfo_list, sockopt, timeout):
        err = None
        for addrinfo in addrinfo_list:
            family, socktype, proto = addrinfo[:3]
            sock = socket.socket(family, socktype, proto)
            sock.settimeout(timeout)
            for opts in DEFAULT_SOCKET_OPTION:
                sock.setsockopt(*opts)
            for opts in sockopt:
                sock.setsockopt(*opts)
    
            address = addrinfo[4]
            err = None
            while not err:
                try:
>                   sock.connect(address)
E                   ConnectionRefusedError: [Errno 111] Connection refused
```

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

tests/test_connection.py

@@ -4581,6 +4581,11 @@ def recv(self, maxlen):
             self.recvbuf = self.recvbuf[maxlen:]
             return ret
 
+    # There can be a delay between the printing of "Websocket Secure Server Started"
+    # and actually binding the port.  There's no obvious way to delay that message
+    # it's done.  So we sleep here.
+    time.sleep(10)
+
     wss = BindWebSecureSocket('localhost', wss_port)
 
     lconn = wire.LightningConnection(wss,