Fixing task callback

src/crewai/crew.py

@@ -354,7 +354,8 @@ class Crew(BaseModel):
     def _set_tasks_callbacks(self) -> str:
         """Sets callback for every task suing task_callback"""
         for task in self.tasks:
-            self.task_callback = task.callback
+            if not task.callback:
+                task.callback = self.task_callback
 
     def _interpolate_inputs(self, inputs: Dict[str, Any]) -> str:
         """Interpolates the inputs in the tasks and agents."""