[3.11] GH-98539: fix ref cycle in _SSLProtocolTransport after close (GH-98540) (#98551)

GH-98539: fix ref cycle in `_SSLProtocolTransport` after close  (GH-98540)
(cherry picked from commit 62bf5d8)

Co-authored-by: Kumar Aditya <[email protected]>

Author: miss-islington

Lib/asyncio/sslproto.py

@@ -107,8 +107,11 @@ def close(self):
         protocol's connection_lost() method will (eventually) called
         with None as its argument.
         """
-        self._closed = True
-        self._ssl_protocol._start_shutdown()
+        if not self._closed:
+            self._closed = True
+            self._ssl_protocol._start_shutdown()
+        else:
+            self._ssl_protocol = None
 
     def __del__(self, _warnings=warnings):
         if not self._closed: