Use logging.warning instead of deprecated/removed logging.warn method

[ethagnawl]

This change set replaces logging.warn with logging.warning in seeder.py.

AFAICT, the warn method was initialled deprecated in Python 3.3 and finally removed by Python 3.11.

I think setup.py may also need to be modified but let's discuss. In the meantime, I can verify that this branch works in a project which is testing Python 3.13rc0.