chore: Restrict GraphServer to localhost traffic only in Jupyter mode (#220)

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Fixes #<issue_number_goes_here> 🦕

Author: ericfe-google

bigquery_magics/graph_server.py

@@ -315,7 +315,7 @@ class ThreadedTCPServer(socketserver.TCPServer):
             # Daemon threads automatically terminate when the main program exits
             daemon_threads = True
 
-        with ThreadedTCPServer(("", self.port), GraphServerHandler) as httpd:
+        with ThreadedTCPServer(("127.0.0.1", self.port), GraphServerHandler) as httpd:
             self._server = httpd
             self._server.serve_forever()