Use log.warning() from the logging library

Every time I run a large chunk of neutron unit tests, for
example:

$ tox -e py310 -- neutron.tests.unit.plugins.ml2.drivers

I see this warning (it doesn't cause a failure):

Captured stderr:
~~~~~~~~~~~~~~~~
    .../neutron/.tox/py310/lib/python3.10/site-packages/ovs/db/idl.py:1484:
  DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    vlog.warn("error parsing column %s in table %s: %s"

Looking at the OVS python library code it seems perfectly fine.

Backtracking, I was able to find the offending code that
actually lived in ovsdbapp. It is a little bit obfuscated
as it was re-mapping the OVS library vlog.Vlog.warn() call
to log.warn(), but I was able to test my theory by modifying
code in my local neutron .tox directory and the warning
went away.

I was never able to narrow things down to a single test, or
class, or file, even running with '--concurrency 1', so I
do not know exactly how this code is getting exercised,
there could be a test that is not cleaning-up properly,
maybe some day we will figure that out.

TrivialFix but not TrivialToFind

Change-Id: Ic6256b4bab48298fe599b7904e9edb0e35b93ce4

ovsdbapp/backend/ovs_idl/vlog.py

@@ -31,7 +31,7 @@ _LOG = logging.getLogger(__name__)
 # Map local log LEVELS to local LOG functions
 CRITICAL = _LOG.critical
 ERROR = _LOG.error
-WARN = _LOG.warn
+WARN = _LOG.warning
 INFO = _LOG.info
 DEBUG = _LOG.debug