Fix test case (#7744)

Signed-off-by: Binbin Lv <binbin.lv@zilliz.com>

tests/python_client/testcases/test_connection_20.py

@@ -765,6 +765,7 @@ class TestConnect:
         method: disconnect a connected client, disconnect again
         expected: raise an error after disconnected
         '''
+        with pytest.raises(Exception) as e:
             dis_connect.close()
 
     @pytest.mark.tags(ct.CaseLabel.L2)