Fix docs build

Author: kevin-bates

jupyter_server/gateway/gateway_client.py

@@ -18,6 +18,7 @@
 from jupyter_events import EventLogger
 from tornado import web
 from tornado.httpclient import AsyncHTTPClient, HTTPClientError, HTTPResponse
+from tornado.httputil import HTTPHeaders
 from traitlets import (
     Bool,
     Float,
@@ -40,9 +41,6 @@
 STATUS_CODE_KEY = "status_code"
 MESSAGE_KEY = "msg"
 
-if ty.TYPE_CHECKING:
-    from tornado.httputil import HTTPHeaders
-
 
 class GatewayTokenRenewerMeta(ABCMeta, type(LoggingConfigurable)):  # type: ignore[misc]
     """The metaclass necessary for proper ABC behavior in a Configurable."""