fix: Prevent callback validation ValueError from being suppressed

- Move signature parameter count validation outside try-except block
- Only catch exceptions from inspect.signature(), not validation errors
- Ensures invalid callbacks properly raise ValueError instead of passing silently
- Addresses final Cursor Bugbot issue with callback validation bypass

This resolves the remaining CI issue where the try-except block was too broad
and caught the ValueError that should propagate for invalid callback signatures.

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

src/crewai/crew.py

@@ -554,12 +554,13 @@ class Crew(FlowTrackable, BaseModel):
             
             try:
                 sig = inspect.signature(self.task_ordering_callback)
+            except (ValueError, TypeError):
+                pass
+            else:
                 if len(sig.parameters) != 3:
                     raise ValueError(
                         "task_ordering_callback must accept exactly 3 parameters: (tasks, outputs, current_index)"
                     )
-            except (ValueError, TypeError):
-                pass
         
         return self