fix: gracefully terminate the future when executing a task async

* fix: gracefully terminate the future when executing a task async

* core: add unit test

---------

Co-authored-by: Greyson LaLonde <greyson.r.lalonde@gmail.com>

lib/crewai/tests/test_task.py

@@ -1727,3 +1727,24 @@ def test_task_output_includes_messages():
     assert hasattr(task2_output, "messages")
     assert isinstance(task2_output.messages, list)
     assert len(task2_output.messages) > 0
+
+
+def test_async_execution_fails():
+    researcher = Agent(
+      role="Researcher",
+      goal="Make the best research and analysis on content about AI and AI agents",
+      backstory="You're an expert researcher, specialized in technology, software engineering, AI and startups. You work as a freelancer and is now working on doing research and analysis for a new customer.",
+      allow_delegation=False,
+    )
+
+    task = Task(
+      description="Give me a list of 5 interesting ideas to explore for na article, what makes them unique and interesting.",
+      expected_output="Bullet point list of 5 interesting ideas.",
+      async_execution=True,
+      agent=researcher,
+    )
+
+    with patch.object(Task, "_execute_core", side_effect=RuntimeError("boom!")):
+      with pytest.raises(RuntimeError, match="boom!"):
+        execution = task.execute_async(agent=researcher)
+        execution.result()