Fix a bug in _update_manager_tools() where, when a task had an assigned
agent in hierarchical mode, the delegation tools were configured to only
allow delegation to the assigned agent itself ([task.agent]), making
delegation circular and ineffective.
Now delegation tools correctly target all OTHER agents in the crew
(excluding the assigned agent), enabling proper task delegation in
hierarchical process mode.
Fixes#4783
Co-Authored-By: João <joao@crewai.com>