Fix DeprecationWarning with patched python-json-logger

Running tests with https://github.com/nhairs/python-json-logger 3.1.0
produces:

  DeprecationWarning: pythonjsonlogger.jsonlogger has been moved to pythonjsonlogger.json

It's easy enough to be compatible with both.

jupyter_events/logger.py

@@ -12,7 +12,10 @@
 from datetime import datetime, timezone
 
 from jsonschema import ValidationError
-from pythonjsonlogger import jsonlogger
+try:
+    from pythonjsonlogger.json import JsonFormatter
+except ImportError:
+    from pythonjsonlogger.jsonlogger import JsonFormatter
 from traitlets import Dict, Instance, Set, default
 from traitlets.config import Config, LoggingConfigurable
 
@@ -171,7 +174,7 @@ def _handle_message_field(record: t.Any, **kwargs: t.Any) -> str:
                 del record["message"]
             return json.dumps(record, **kwargs)
 
-        formatter = jsonlogger.JsonFormatter(  # type:ignore [no-untyped-call]
+        formatter = JsonFormatter(  # type:ignore [no-untyped-call]
             json_serializer=_handle_message_field,
         )
         handler.setFormatter(formatter)