fix: resolve CI failures for fallback LLM implementation

- Fix type checker error by adding None check before raising last_exception
- Fix ContextWindowExceededError constructor with correct signature (message, model, llm_provider)
- Update auth error test assertion to match new print message format

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

tests/agent_test.py

@@ -1984,7 +1984,7 @@ def test_crew_agent_executor_litellm_auth_error():
         )
 
     # Verify error handling messages
-    error_message = f"Error during LLM call: {str(mock_llm_call.side_effect)}"
+    error_message = f"Primary LLM failed: {str(mock_llm_call.side_effect)}"
     mock_printer.assert_any_call(
         content=error_message,
         color="red",

tests/test_agent_fallback_llms.py

@@ -133,7 +133,9 @@ def test_agent_fallback_context_window_error():
     with patch.object(primary_llm, 'call') as mock_primary, \
          patch.object(fallback_llm, 'call') as mock_fallback:
         
-        mock_primary.side_effect = ContextWindowExceededError("Context window exceeded")
+        mock_primary.side_effect = ContextWindowExceededError(
+            message="Context window exceeded", model="gpt-4", llm_provider="openai"
+        )
         mock_fallback.return_value = "Fallback response"
         
         result = agent.execute_task(task)