fix-python-websockets#762: support py3.9 deprecation warning with new py3.8 api (create_task)

Author: DavidBord

src/websockets/server.py

@@ -715,7 +715,9 @@ async def _close(self) -> None:
         if self.websockets:
             await asyncio.wait(
                 [
-                    asyncio.create_task(websocket.close(1001))
+                    websocket.close(1001)
+                    if sys.version_info[:2] < (3, 8)
+                    else asyncio.create_task(websocket.close(1001))
                     for websocket in self.websockets
                 ],
                 loop=self.loop if sys.version_info[:2] < (3, 8) else None,