fix: add 'task' (singular) to TRACE_EXCLUDE_FIELDS

agent_execution_error and task_failed events have a task: Any field
holding a full Task object. 'tasks' (plural) was excluded but 'task'
(singular) was not, so the full object leaked through serialization.

lib/crewai/src/crewai/events/listeners/tracing/trace_listener.py

@@ -134,6 +134,7 @@ TRACE_EXCLUDE_FIELDS = {
     "crew",
     "agent",
     "agents",
+    "task",
     "tasks",
     "context",
     # Heavy fields not needed in individual trace events