Log warning when event serialization fails in msg_to_dict

This commit updates the `msg_to_dict` exception handling path to
fire a warning level event instead of raising an exception.
Truthfully, we're not sure if this exception handling path is even
possible to hit. That's because we recently switched from betterproto
to google's protobuf. However, exception path is the subject of
[CT-2264](#7113). Though we
don't think it's actually possible to hit it anymore, we still want
to handle the case if it is.

core/dbt/events/functions.py

@@ -2,7 +2,7 @@
 from dbt.events.base_types import BaseEvent, EventLevel, EventMsg
 from dbt.events.eventmgr import EventManager, LoggerConfig, LineFormat, NoFilter
 from dbt.events.helpers import env_secrets, scrub_secrets
-from dbt.events.types import Formatting
+from dbt.events.types import Formatting, Note
 from dbt.flags import get_flags, ENABLE_LEGACY_LOGGER
 from dbt.logger import GLOBAL_LOGGER, make_log_dir_if_missing
 from functools import partial
@@ -219,7 +219,9 @@ def msg_to_dict(msg: EventMsg) -> dict:
         )
     except Exception as exc:
         event_type = type(msg).__name__
-        raise Exception(f"type {event_type} is not serializable. {str(exc)}")
+        fire_event(
+            Note(msg=f"type {event_type} is not serializable. {str(exc)}"), level=EventLevel.WARN
+        )
     # We don't want an empty NodeInfo in output
     if (
         "data" in msg_dict