SwarmConn: don't access Swarm.manager

Open a local nursery instead.

libp2p/network/connection/swarm_connection.py

@@ -56,13 +56,14 @@ class SwarmConn(INetConn):
 
     async def _handle_new_streams(self) -> None:
         self.event_started.set()
+        async with trio.open_nursery() as nursery:
             while True:
                 try:
                     stream = await self.muxed_conn.accept_stream()
                 except MuxedConnUnavailable:
                     break
                 # Asynchronously handle the accepted stream, to avoid blocking the next stream.
-            self.swarm.manager.run_task(self._handle_muxed_stream, stream)
+                nursery.start_soon(self._handle_muxed_stream, stream)
 
         await self.close()