fix: Replace deprecated .warn method with .warning

The `logging.Logger.warn` method has been deprecated since Python 3.3
and is due to be removed all together in Python 3.13. See
python/cpython#105377

`logging.Logger.warning` is the preferred and recommended way to log
warnings.

Fixes openedx/public-engineering#149

openedx/core/djangoapps/user_authn/views/login.py

@@ -402,7 +402,7 @@ def _check_user_auth_flow(site, user):
             # we don't record their e-mail in case there is sensitive info accidentally
             # in there.
             set_custom_attribute('login_tpa_domain_shortcircuit_user_id', user.id)
-            log.warn("User %s has nonstandard e-mail. Shortcircuiting THIRD_PART_AUTH_ONLY_DOMAIN check.", user.id)  # lint-amnesty, pylint: disable=deprecated-method
+            log.warning("User %s has nonstandard e-mail. Shortcircuiting THIRD_PART_AUTH_ONLY_DOMAIN check.", user.id)
             return
         user_domain = email_parts[1].strip().lower()