Address review: async task logging, fix typo, use _get_agent_to_use for role

- Add completion/handoff logs for async tasks in _process_async_tasks
- Fix pre-existing filter_headeruvs typo back to filter_headers
- Use _get_agent_to_use() instead of task.agent.role in skip path
  to match the effective agent used during execution

Co-Authored-By: João <joao@crewai.com>

tests/crew_test.py

@@ -1123,7 +1123,7 @@ def test_kickoff_for_each_empty_input():
     assert results == []
 
 
-@pytest.mark.vcr(filter_headeruvs=["authorization"])
+@pytest.mark.vcr(filter_headers=["authorization"])
 def test_kickoff_for_each_invalid_input():
     """Tests if kickoff_for_each raises TypeError for invalid input types."""