Tango logger "warning" method

The object returned by self.get_logger() in a tango device appears to be something like a python Logger object and can be mostly used as such. However, in later python versions, the warn() method has been deprecated (see https://docs.python.org/3/library/logging.html#logging.warning) and replaced by warning() which does not appear on the pytango Logger object. In the interest of forward compatibility I suggest it should be added. The warn() method could of course be kept. As far as I can tell the methods should do exactly the same thing.

PyTango version: 9.5.0