fix(mge/optimizer): use static key to avoid mem leak

GitOrigin-RevId: 85298084a337b4caa4aafb601259cf18ef3df557

python_module/megengine/optimizer/optimizer.py

@@ -225,13 +225,13 @@ class Optimizer(metaclass=ABCMeta):
                     param.grad.reset_zero()
 
     def bcast_param(self):
+        key = 0
         for group in self.param_groups:
             for param in group["params"]:
                 bcast_param(
-                    param,
-                    "bcast_param_" + str(get_group_id()),
-                    is_root=(get_rank() == 0),
+                    param, "bcast_param_" + str(key), is_root=(get_rank() == 0),
                 )
+                key += 1
 
     def state_dict(self) -> Dict:
         r"""Export the optimizer state.